Mechanism to temporarily connect different pitch stake pins (2.54mm and 1.27mm)?
There are several ways to approach the problem, but what I would do (and I do), is to keep some male/female headers with a 1.27mm and 2.54mm pitch always in the drawer together with some wirewrap wire. In that way, when the issue comes up, it doesn't take long to create a bridge cable to convert from one pitch/pinout to the other.

With a bit of practice, it is not too hard to solder on a 1.27mm connector.