Replace solid axle with quick release on Fixed Gear This goes off a previous question:

Quick Release on Fixed Gear Bike

Suppose I want to replace my solid axles with quick release skewers on my fixed gear bike. Yes, I am aware that this isn't necessarily recomended, but done right it should be fine (i.e. enclosed cam qr skewer, chain tensioner like surly tugnut). 

The spacing in the rear 120mm, what kind of quick release skewers do I get? I can't seem to find any with 120mm spacing. Is it simple to buy one that is ~130mm and shorten it? How do you do that? 

Relavent links:

http://sheldonbrown.com/fixed-conversion.html#qr

http://www.bikeforums.net/singlespeed-fixed-gear/704523-quick-release-fixed-gear.html
This is easily accomplished, simply replace the axle from your wheel with a QR axle, at most you may have to cut an axle/skewer to length and maybe cut more threads if you can't find an axle and skewer with enough thread on it. But you'll need to be comfortable with cutting metal and have the right die set. 

 

If you try shopping around for a 120mm rear QR axle, you'll have better luck looking for a complete hub and just parts it. They're not super common though, and not cheap...