The kefir grains are a culture of bacteria and yeast that are active at near-room temperatures.
Their ideal temperature is 71F (22C).
Below this and they will grow too slowly.
Above this temperature, up to 86F, for extensive periods the grains will be damaged.
http://users.chariot.net.au/~dna/kefir-faq.html#temperature Building the grains takes time- there's no way around it.
You can keep the grains at exactly 71F to maximize their growth.
You can also change the milk often and keep the milk to grain ratio high to ensure that the milk doesn't acidify too quickly and the grains stay active.
You may see an improvement using organic milk as it won't have residual antibiotics in it.
http://users.chariot.net.au/~dna/kefir-faq.html#growthrate
I have not read anywhere of a way to modify the milk itself to encourage growth.
You might experiment with adding a small amount of milk powder to make the milk more nutritionally dense but my gut feeling is that this would have a negligible effect if any.
I'm afraid your friends are just going to have to wait patiently.
cooking.stackexchange.com/users/2001/Sobachatina
For good milk kefir grain growth use a shallow wide container to grow your kefir grains.
This will give each of the grains more access to feed on the milk instead of clumping up at the top of a narrow jar and only a few being free in the milk.
You can also stir the culturing kefir a few times during the day dispersing the kefir grains through the milk.
Don't skimp on the quantity of milk used.
Milk kefir grains love Full cream milk.
and yes, raw organic full cream milk grows the best milk kefir grains.
cooking.stackexchange.com/users/10373/Marg Black
I have got a jar of kefir going that is made with whole milk powder.
The grains seem to grow a lot faster then even with whole milk from the farmer.
Try it, you don't have much to loose.
cooking.stackexchange.com/users/18962/Christel Webb
I made mine grow by adding it to half and half milk and then to cream.
Alternated this and the tiny little grains were swollen like cauliflower pieces.
cooking.stackexchange.com/users/24269/Jenn
I started making kefir 2 weeks ago, with 1 large grain.
Not being certain about quantities, I used 2 cups of milk in my first batch.
30 hours later, I had cultured milk.
As those quantities and time frames worked, I have just continued with that, although the time is now down to almost 24 hours of culturing.
In between I made a batch of yummy sour cream, (popped my grain into a cup of whole cream).
Clearly the grain loved the fat in the cream, it multiplied and cultured within 30 hours!!
I have since given the new grain away to a friend, but the one grain I kept (my large and original one),is doing a great job of culturing 2 cups a day.
cooking.stackexchange.com/users/29809/Averil
I would go with a shallow wide container, and since kefir feeds on lactose, you can add powder milk to natural whole milk to increase the lactose in the mix.
It should give your kefir colonies more food to process.
cooking.stackexchange.com/users/50821/hector
It's about two weeks that I make Kefir at home. I started with three mid-size Kefir grains, and now I have six ones (three of them are really big)  Now my friends get interested in making Kefir too. But I don't have enough Kefir grains to share with them.  Is there any quick method for cloning Kefir grains? For example, keeping them in warmer place, giving them richer milk, or something like that?
Fastest way for cloning Milk Kefir Grains
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<milk><kefir>
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cooking.stackexchange.com/users/9780/Aidin
Keep the grains at exactly 71F to maximize their growth, change the milk often and use enough milk to slow acidification and keep the grains active. Kefir feeds on lactose, so use full cream milk, half and half or cream, or add powdered milk to natural whole milk to increase the lactose. Keep the grains at 71°F and change the milk often. Use full-fat milk or cream and try adding powdered milk to increase the lactose.
Keep the grains at 71°F to increase growth. Change the milk often and use full milk cream or even full cream. Increase the lactose by adding powdered milk.