Speak to your saddle fitter, as it's more than likely they can come up with a compromise. If they can't, I'd be more concerned TBH. Yes, riding in all gaits is the ideal but it may not always be possible for a host of reasons.
I recall not riding P out of walk for a saddle fitting appointment (possibly a few?) when he was going through a sharper than a sharp thing phase, was still working through his issues and generally needed some extra support in life. He did take it upon himself to show some shapes so we definitely ended up doing more than walk but it wasn't planned
I did speak to saddle fitter before hand and they knew him & his history, so it was fine - I said I won't get on unless P gives me a green light too, which I didn't always get and wasn't going to necessarily risk it for a fitting. Remember, they don't want you to go splat on their books, anymore than you do! Too much paperwork for them for a start
From memory, the fitting was done assessing the fit without a rider, then on the lunge and then with me onboard and they saw what they could.
I think we probably booked appointments to come back & check more frequeny than normal but couldn't swear to it? It was a few years ago now.
Yes, we obviously had to trot and canter at some point - but back then, his reactions were hugely day to day dependent and with a sensitive horse with 'history' we cracked it at our own pace without the pressure of needing to do X on X day.
I'm sure there will be ways round it - the saddle fitter might just caveat a few more things too.