You can do that already, at least on the website using Chrome as my browser.
Suggestion: Play the Bots from any position
Sort:
The option shows up after you have chosen to play the computer. Run your cursor down to that line of little symbols; the first one, "change bot" is what you want.
So When doing analysis of positions/games there is always the option to finish this game vs the computer. My suggestion is just to expand this so that you can play the position vs any of the bots and not just the 3200 level AI.