Is this on server? If so, one option might be to redirect the workbook to itself.
Thanks Ben, This is both server and desktop. I'm not sure if I follow on redirecting the workbook to itself. Could you elaborate on what you mean?
I'm not sure if you still need help with this, but as I was searching for an answer to a similar question and I came across your post and thought I would share with you what I found.
For my workbook, I needed to show the URL action on just one value in my dimension.
Text needed on URL='Building1234Page'
My 'Building for URL' calculation looked like:
if [Building Number]='1234' then "Building1234Page' else "" end
My URL Action is set up so that the URL looks like "www.thisisafakepage.com<Building for URL>".
Using the action set up that way makes it so the hyperlink for my URL action only shows up on the tool tip of the marks where [Building Number]='1234'.
I hope that helps!