Interesting question - couldn't resist trying to map some options
including malky's to see what sort of difference there would be.
As malky notes, there are options - most involve some pathless sections and some height gain so depends on how much you're wiling to accept.
Going by road A93 suggests 25km and 400m ascent so that's probably the most efficient.
Going up the east comes in at about 29km but the ascent is 940m
Combining west and east is longer at 33km but reduces the ascent to 790m
Going up the west and over Morrone decreases distance to 30km but ascent back up to 880m
Staying in the west but going to Inverey increases distance to 32km but ascent drops to 670m
Please note that all are approx and are off the map so actual ground conditions may vary. From my own limited experience of the area, I found off path walking fairly straightforward but the conditions were quite dry at the time.