Hi mate, I'm in the very same situation as you, trying to fit 5x100 wheels to my b7 avant
Check the offset of your new wheels. If it is anything around +40, I would think you will get away with buying a set of 15mm adaptors, venom motorsport do them. I bought a set from them, but as my wheels are et35, they were sticking out too far beyond the arches.
I have gone down the road of redrilling the hubs. It's not an easy road to go however, I've had to buy two new front hubs, as the oem ones don't suit redrilling as there is not enough thickness between the original bolt holes to allow new holes to be drilled in between. Confused yet? I will post pictures of progress tomorrow.