adding and deleting can be done 100% manually using the CUSTOM folders for BootWiz rather than using the console. The console ONLY adds (or deletes) the folders under CUSTOM for 32/64 bit drivers. That's it.
When the WIM is assembled by Bootwiz, if you look at the logs, it actually calls DISM to inject the drivers into the WIM, so the syntax is both exposed there in the BW logs, and you can look up the DISM call for it in Technet or something.
That said, neither DISM nor BootWiz will successfully navigate EXE's in a driver. EXE's are never used as part of adriver as far as I'm aware, but you may know differently. Drivers are, per MS, sys files, DLL's, etc, not EXE's. But things change, right?
SOOOOOO
IF you feel you really have a valid driver and we're not processing it in the console, just make the folder manually in the CUSTOM folders under BootWiz and see if DISM will take it even if BW does not. :D Worth a try, right? The logs will show if DISM failed or not on that driver, and if it fails, no big - it goes on anyway...