I have been running my K75 for about a year now, and have just discovered that someone had treated the fuel tank with tank sealer. That in itself is not terribly traumatic, but the problem is that it is beginning to come loose from the inside of the tank. Any tips on what to do about this? I realize that there is a good screen on the intake, but I don't want it to get to the point where pealing bits of this stuff get into the fuel system.

How many times have I seen tank sealant peeling off. I don't think that there is a truely successful one yet.
It will be difficult for you to remove that stuff as some of it will stay in place for a long time yet. I would not be too concerned about it getting through the pre pump filter as it usually just remains in large chunks.
The sealant has probably been used to seah the corosion that occurs under the pump area and sometimes in the same place on the other side of the tank.
The best stuff I have found is a product from permatex and it is used just on the affected area on the outside of the tank so it is an easy fix and you could use it when your tank starts leaking again.
http://www.permatex.com/products/product-categories/specialized-maintenance-repair/professional-repair-systems/permatex-fuel-tank-repair-kit-detail

A local sealant like that would probably be the best solution. I will use the bike this summer and then in the off season, take off the tank and, after removing the (innards) get all of that stuff off that's loose and just live with it. I need to get in there to fix the fuel light sensor anyways at some point. It probably isn't worth the cost to me to replace the tank as long as it won't screw up anything in the fuel system.

Now that looks interesting. I like the idea of sloshing around some pea gravel in the tank to remove any loose sealer.