> Any tips for doing something like this with the existing tool?
Not possible the case you exactly describe it. (Although this feature has been requested for many years and I haven't tried the latest version of msi)
But...
I assume that your intent is to build a db file (i.e. use dbLoadTemplate). In that case, they are specific shell tricks (i.e. how template and substitution files are built) and iocsh/iocinit tricks (i.e. how the files are used to populate the EPICS database).
Can you show us your real template? and possible substitution entries?