Thanks, all! Really appreciate all the suggestions.
In the end, I decided to just bag the poll in this case. Interestingly, I got a handful of likes already to the topic without even asking for it, so people seem enthusiastic and are showing it. 
I do think that down the road it might be of value to allow one option to choose from, but it’s not a high priority for me. Perhaps someone else wants to make it possible at some stage. The 100% showing issue seems to be the only potential snag, beyond the UX tweaks that would be needed.