In an ideal world you’d stick with what has worked in the past. From the sounds of it that’s not going to happen this time around. I assume your climb is going to be technically challenging and more physically demanding then dragging a sled up the West Buttress.
You’re going to be well acclimated with all the time above 14,000ft that you are likely to be doing. That’s a good thing and can go a long way towards compensating for a small drop in fitness. It’s not like you’ll be doing nothing for those 3 weeks.
For added training stress you might be able to carry a heavier load on some of the days.
Other than this I can’t think of another way to get in extra training time other than ditching the clients for a couple hours on some days.