I have a 113mm, and it is 5mm short (drive side) to get the right chainline and clearance of the seatstay.
Most of the ISIS BB manufacturers only have 118mm, anyone has one with about 123mm spindle length?
If you find a NDS BB cup that will fit inside a 68mm shell(I'm assuming you have a 68 because there are plenty of 123x73 ISIS BB's out there) you'll be fine. There just needs to no outer lip to the cup and it needs to be able to sit flush with the BB shell. I've done this with customer bikes at the shop I work at and I have yet to have any issues with it.