One suggestion is to strictly separate Pbind / Pdef definitions and the Pspawner flow-of-control code, e.g. your main file might look like:
(thisProcess.nowExecutingPath.dirname +/+ "section1defs.scd").load;
(thisProcess.nowExecutingPath.dirname +/+ "section2defs.scd").load;
...
p = Pspawner({
...
});
… where the Pspawner just refers to resources by name.
It doesn’t solve the problem of transitions, but it does mean you have a zoomed-out view of the form in the Pspawner, and you can zoom in to detail in the auxiliary files.
hjh