Is there a way to also use kegerator for lagering or do I need a 3rd fridge??

I want to be able to brew lagers, but also have kegs in the kegerator at the same time. How would I do that without buying one more fridge just for lagering fermentation? Thanks in advance. 3 fridges side-by-side would have been an overkill

Lager fermentation temps are usually OK serving temps. (For most styles anyway...) And while your lagering you just have to let your finished beers warm a little before enjoying.

Thanks for a sound advice! I will do just that
Is there a good and proven write-up on the easiest way (and/or tool) to temp-control a fridge? Sorry, I am new to this. My fridge is not-so-old Maytag (with energy saver mode and things like that)

Depending on what you value your time at, get something like this:
http://www.amazon.com/dp/B003X01C7O/?tag=skimlinks_replacement-20 (ignore the reviews, you have to wire it. Super easy, just youtube and watch somebody do it with you step by step)

Or if you're on a tight budget and want to do more indepth wiring/programming, lot's of guys do the ebay control:
https://www.homebrewtalk.com/f51/ebay-aquarium-temp-controller-build-163849/

I have used a few of the Ebay controllers and for their price, they are super simple. Only down side is the readings are in celsius, but a nice conversion print out with the main temps you are looking for alleviates that issue.

Lagers are generally fermented at about 50 degrees (give or take two degrees either way). That's too warm for my taste for my kegerator, but they are lagered (cold stored) after fermentation at near freezing if possible. I lager at 34 degrees for about 6-10 weeks for most of my lagers. Unfortunately, that's a bit too cold for my kegerator. But I can make do by letting my tap beers warm up a bit before drinking them.