If you have come all that way an extra couple of hous up the A82 and you are on the proverbial doorstep & won't waste 2 days circumnavigating the Mull & back...... You could also use the extra road miles to take in some land locked stills. Having said that, you could use the to / from trips to do Campeltown & Arran. (beware the walk from the pier on Arran!)
Not that I have been giving this little escapade some thought myself or anything....
Summary:
Islay: Three could be got from one pier by a short stroll, another three have easy rib access, and one (Kildonan) will either need a spring tide visit with a long walk & a very long wait for the tide to come back in or a cab.
Oban: Easy, could even do it before you launch if you drove the extra few miles!
Nevis: Bit of a walk from anywhere I would leave the boat, but a short cab ride from the canal basin.
One issue you may have with doing it in Oct / Nov is a lot of them close down for visits outside the "tourist season" so you may not get in .....
and of course it would be rude not to stop at the microbreweries on Colonsay & Easdale as well which in turn gives a perfect excuse for going via the Corry-v.....