So often get at cross purposes when communicating this way, put it down to my crappy language skills...
Anyways, my initial plan of bouncing through a mono group is that you bypass all panning thus pan law stops being an issue.
Try this, Create a mono group channel, name it mono bounce or whatever and set it's fader to +3db but assign no outputs to it, actually at this point forget about it, certainly don't send anything to it.
Do your mix as normal till you want to print some mono tracks.
Then route the tracks you want to bounce to the mono group (still no output though) and select that group channel from your export audio. Done!
Only use the mono but when you're actually bouncing, the rest of the time forget about it.
Re the bounces no passing the null test: I think that's because any change in the clip volume or in the mixer, including pan, channel fader, master fader and even pan law settings, is processing the file through the (64bit?) mix engine and then being printed at whatever resolution your export is set at.
It won't Null, even if you dither it, won't be 'exactly' the same, but really you won't hear it and as JMCecil said "this stuff is at the who gives a crap level".
Someone correct me if I'm wrong, but I think I'm remembering my digital audio theory correctly!
DAW W7 32Bit-Cubase 7.0.6-Wavelab 8.0.2-Core2 Quad Q9400-4 Gb Ram-Lots of HDD's-Dual Monitors-Old, but solid! Interface AD/DA Focusrite Liquid 56 (Mix Control 3.2)-Focusrite Octopre Platinum (Via Twin Light-pipe)-DBX 386 dual valve Pre (Via AES/EBU)Monitoring Genelec 1029A's-Yamaha HS10W Sub Console Yamaha PM2000 24/8-146kg of analogue goodness