Steam Heating: Correcting a Back-Pitched Pipe?

I have a thread on the Building & Construction forum that includes a plumbing issue and I'd be appreciative if some plumbers would have a look at give their opinion.

http://www.diychatroom.com/f19/repair-damaged-ceiling-joist-split-check-405089/#post3353657

The problem regards a steam radiator system: a 2" heating pipe that feeds a radiator is back-pitched, allowing condensate to pool in the pipe and causing pipe hammering noise. The pipe in question is routed under the floor and passes through a couple joists. I'm assuming the hole would need to be raised vertically 1'-2" (or a new hole made elsewhere) to permit the pipe to be pitched correctly so as to angle downward towards the heating steam riser pipe.

The problem is how would a plumber typically go about doing this sort of pipe repositioning without structurally weakening the joist?

Thanks a bunch!
Lovegasoline