You can also retrofit mini H1's in to the housing without cutting the reflector. Here's a link for a cheaper option.
MK4 mini H1 conversion
I will add that the additional extension out the back of my housing due to the d2s retrofit is only the thickness the bulb plug itself, maybe 1-1.5inches. The passenger side required no modifications and fits just fine. The whole process was straight forward with the supplied harness other than getting the PVC bushing in to the correct place. I cut the hole slightly big in the reflector for some wiggle room and installed the lights back in to the car. Then set up a reference piece of cardboard to get the lights adjusted properly, hot glued everything in place and took them back out to final JB weld them in. As the picture shows I blacked them out and sealed the lights back up, put them back in the car and adjusted properly with the normal headlight adjustment screws.
It took me about 2 weekends total with interruptions from the kids but that was the benefit of buying additional cheap ebay housings to not have any car downtime. I haven't had any issues with moisture/leaks as I've seen before from cheap housings but I made sure they were completely sealed in any possible spot.