It seems that with the addition of layout based transposition overrides in version 3.5, one could “fake” a capo on an alternate guitar (or other CAPO-able) part using the following steps (using capo on 4th fret of a standard tuning steel-string guitar as an example):
If using tablature, use the “Edit Strings and Tuning” dialog to tune up all strings up 4 semitones (reduce the number of frets per strings as well if you wish)
On the capo guitar layout, use “Set Clef and Transposition Overrides” to set "Written Middle C sounds like an E.
From the quick experiment I did, it looks traditional notation, tabs and chords transposed currently. Might this be a viable workaround?