What if we cut Aber a day short and did G&S on Saturday (seeing the Mikado done by the main troupe instead of Pinafore done by a minor troupe), spend Sunday morning at the G&S fair, make it back to London Euston Sunday night (we can leave the luggage at the station and have dinner somewhere), ride the sleeper train to Inverness (thus eliminating the 'take whole day doing nothing but sit on a train' thing), then went to Lewis on Monday.
though, argh, we'd get into Inverness 20 minutes *after* the morning bus to Ulapool. Is there another way to Ulapool? Scotland's transit system hates us apparently.
If not, well, there's luggage storage at the Inverness train station. We wouldn't make it to Lewis until 8pm though.
Spend Monday night and all tuesday on lewis, and the train times on Wednesday match up to the bus ever so much better.
That is if you think you can sleep on a train.
this plan also lets us stay up late at the G&S cabaret and not have to get up stupidly early the next day to rush to trains. and still leave aber at the reasonable hour of 11am