You may have clearance problems using a chain tool on the link going into the bar stock. I broke a chain whip once (on a SEVERELY rusted-on lock-ring), and tried to use a chain tool to re-attach the chain section to the bar part of the whip, with limited success and a lot of cursing. Don't remember exactly what the problem was, and it's not in front of me now, but I remember it being an issue.

Thing is, just the old chain, with enough coming off either end to wrap a rag around and death-grip with your hand, might do the trick. If it's just for cassette lock-ring removal, those rings aren't supposed to be reefed down very tight. They're not tightened by rotation like a freewheel, and the knurles on it and the smallest cog keep it from loosening.