Cameron my boy , you will worry yourself into an early grave.
Yes its nice if the donk gets a run every couple of weeks but shoot, it will not roll over and play dead if it only happens once a month.
Now its also true that a diesel should only be run under load but if you were to go out and let her run for half an hour every week or so you won't kill it. Of course you could just run it at low revs in reverse and hope your mooring is a goodun.
Anywho, I thought you were in a pen ?
ps - Ok so we went solar end of large year but you know us. We are out on Raven at least one weekend in two and we'll spend up to eight weeks a year living on board during our mini cruises. Pre solar we would run the dink up to two hours a day to charge house batteries. Sometimes I'd take the opportunity to go for a potter but most times not under load. That lil ol Bukh gets a bit tick from mechanic each year so it cannot have done the thing much harm.
cheers mate, love to the missus.