Kossel with heated bed - how is it possible?

Hello together,

I've built a mini-Kossel and I've got some serious problems getting the PLA to stick on the glass bed.
After reading in the forums, I've purchased a heated bed MK2b. Long story short, it doesn't fit into the Kossel. It's just about 5mm on each side, but it's 5mm too much. I've already ground some of the heatbed off on both sides (almost up to the copper layer), but it still doesn't fit, the belts are in the way.

So, how did you solve it? Or, if you all are printing without heatbed, just gimme a hint how you got the filament sticking, I can't get it to work...

TIA
stahlsau aka Jan