Yes, I agree, this is probably the only way to handle it at the moment. You'd need to find out a rule (or use a script) to turn the book intros into a sidebar.
Avoiding a sidebar... theoretically it should be possible to drop to monglot from diglot, but it'd need some trial-and-effort to make it work, *IF* you had control of the USFM which is getting to XeTeX.
But there's no process to run a changes text on the merged USFM, and so the process to alter the files is going to be a painful process for you, unless you're very comfortable using a command-line:
It'd look like:
1. Run through PTXprint
2. Quit PTXprint
3. Modify the merged file under {project}/local/ptxprint/....
4. Run XeTeX manually
5. Generate modified TOC definitions if you don't want the basic all-books-in-order
6. Apply whatever postprocessing is needed.
Any modifcation to the text or preprocessing would require you do to it all over again, and you'd need to alter the adjust lists by hand, like in the days pre-ptxprint.