I've seen videos where people put their clownfish in a clear pipe so that the clown pretty much has nowhere to go except in and out of the anemone (temporarily, obviously). Do you think 2 1/2" is wide enough? It's the biggest diameter I can find online.
https://www.amazon.com/POWERTEC-701...TF8&qid=1490208061&sr=8-2&keywords=clear+pipe
https://www.amazon.com/POWERTEC-701...TF8&qid=1490208061&sr=8-2&keywords=clear+pipe