So I've made the mistake of letting MrsH have a go on the Trice XL on the trainer, which necessitated bringing the boom in by 3.5 inches, with adjustments to the chain tubes and taking out a section of chain (plus tweaking the cable length on the front derailleur) - but she liked it, in a type 2 fun kind of way.
So, rather than the faff of changing length every time we swap between us, there seems two options.
1. Get a tensioner to take up the slack. I've seen the Terracycles and the Ice ones, they are quite spendy.
2. Get rid of MrsH, and trade her in for a younger, leggier model with the same inside leg length as me. This is probably more spendy than option 1 though, to be honest.
Going back to tensioners, the ICE one is probably easier to get in the UK, and looks as if it'll automatically adjust the length without relying on springs as it adjusts the chain by twice the boom length difference. Ease of adjustment is pretty critical if MrsH is to do it herself; loosen the boom with the quick releases that come with the kit, adjust to a measured length, tighten, front derailleur onto smallest ring and take up the cable slack is within her skillset. Finding the masterlinks, removing a section of chain without loosing the rest of it up the chain tubes, then rejoining probably isn't going to happen without me there getting oily.
Is there any other easy way of taking up slack I should be looking at?