I understand your interest, as several others in this forum, so please vote the question and ask others to vote it.
That's difficult because you have to "reverse-engineer" into a code that you don't know and that's automatically minimized and put together into a single file that is impossible to debug in a browser.
So, even if you want to dig into the code, you will have first to break all automatic "minimizations" that widgetkit have in place ...
And in the end that might go against the Yootheme license, because that's not GPL code!!!
So, basically the answer is, it's not possible to have auto-height according to the content using the slideshow.
I don't thing that would be a major work to the Yootheme people, because they are already doing some similar in the accordion, but I don't have any indication that they will do this change to the slideshow.
I renewed the subscription because of the tab feature, but now it's useless! I'm really disappointed with this!