Multiple non-thunderbolt monitors to MBP-r '12
I've managed to get my hands on some screens now, and even though Apple representatives said it wasn't possible, it indeed is.

I have now 2 (two) Dell U2515H connected and a Lenovo at the same time. On top of that, the screen on the macbook pro is actually on. 

The setup is as following!

MiniDP (thunderbolt) --> Dell U2515 DisplayPort
MiniDP (thunderbolt) --> VGA adapter --> Lenovo VGA
HDMI --> Dell U2515 HDMI

It also works with thunderbolt --> DVI and thunderbolt --> HDMI

I've attached a photo to documentate this functionality! Happy multi-monitoring!

Picture proof