I'm guessing its a Bic Airflow 175 like this?
www.trademe.co.nz/sports/kites-kitesurfing/kitesurfing/auction-344405392.htmThe problem with very long twintips is that the tail is way behind the backfoot and that can result in you having to pull up more on your front foot to get the leverage. My guess is that with your ankle problems, a short TT would be better.
There are some boards with the footstrap locations offset toward the heel side. They might be an option.
Your best bet is to discuss it with your local kiters. They are quite likely to try to help if asked the right way. You are a unique case, so it may work better to sort it at the beach.
At the end of the day strapless may turn out to be the best option but you are right to explore all the options.