I've had a couple of jobs in which I had to replace toilet flanges in slab floors. The first one took me about two hours. The second I did a complete job in less than 30 minutes! I used an inside pipe cutter to cut the flange flush with the concrete slab. Then I used a chisel to separate the remaining part of the flange from the PVC pipe. It was a little ragged but that didn't matter. I was very careful not to crack or damage the pvc pipe. I found a flange called "twist 'n seal" which has an expanding rubber ring at the base. It will slip into either a 3" or 4" pipe. On a 4" pipe the rubber ring has to be screwed up on the insert to expand it to a snug fit. I just shoved it in the pipe then twisted till very snug, aligned the toilet bolt holes/slots then used "tapcon" screws to anchor to the concrete floor and VOILA.. a super job and with very little experience...VERY FAST. I think you can stretch this to work on a 2" fill. Worst case, use a concrete drill bit and drill holes very close together around the pipe once the flange is removed, then chisel out around the pipe (a hammer drill really helps) add a coupling and short length of PVC pipe and cut flush to floor then install a flange (or "twist 'n seal) that will slip into the pipe. This is relatively easy if you have PVC. If you've got cast iron pipe you've got a tough job ahead of you.