Using trainer as dynamo I was wondering if it is possible to to use a magnetic trainer as a dynamo.

While riding on trainers, at a gym, or at home, I always think to myself, "I wish I could capture all this energy and put it to good use".

Has anyone ever turned a trainer into a dynamo?  If so, I'd like to know what modifications are needed and what tools and parts are necessary, plans, etc.

Moreover, I'd like to know if it is then possible to use this dynamo to supplement power to ones' home, as opposed to just storing it.  While discussing it with a friend, the main challenge that came to mind was converting the current to A/C and synchronizing the phase, voltage, frequency, etc. with the power coming into the house.  Probably a bit overkill if you're not an experienced electrician (which I'm not) but maybe I'm wrong.

If hooking one up to the home is not realistic, is there any simple configuration that one could use to provide useful energy and store it?
You could. If you were a hobbyist, it'd be simple enough to hook a DC motor to act as a generator, smooth the output, boost-buck it to the right voltage, and use it to charge a deep-discharge lead-acid battery.

From there, you could either use it to charge your USB equipment or get an inverter to run some lights. I would not hook it into your mains, the equipment to do so safely is expensive.

I'd estimate the setup would cost just around $200-1000 depending on what parts you already have lying around.

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That said, let's say you already had most of the parts so it only cost you $200.

You could most probably output 100-400 watts an hour. Let's say, you're in very, very, very good health and can do 250 watts for 2 hours a day. That's 500 watt-hours. Over a month, training 20 days that'd be 10,000 watt-hours or 10 kWh. 

In my region, electricity is 20 cents a kWh, so you would be generating $2 a month.

So you would amortize your equipment cost of $200 over 100 months or 8 years. That's if you're in excellent health. 

Note 0: Values chosen for ease of calculation rather than strict adherence to reality. However, I believe they are within an order of magnitude correct.

Note 1:  your energy expenditure will be such that your increased food consumption will likely exceed $2/mo. 

Note 2: if you break or wear out anything, you'd be back to square zero. Even deep discharge batteries have a limited life span.

Note 3: This model doesn't include charge/discharge/inverter inefficiencies. You should most probably multiply everything by 70-80%.

Note 4: this exact scenario was used in an episode of Black Mirror, season 1.