User input to URL with out creating a field

I would like to prompt a user to add a parameter to a URL Formula.

Here is an example:

"https://apimachine.mycompany.com/apps/qbd_update.py?days_back="; & 
 (prompt user for number of days back) & "&token=" & [Mytoken]

We have our own API server that handles the call, but it requires us to provide a number for the parameter "Days Back".  I don't want to create a field for that in Quickbase, I just want to prompt the user for that number in the URL.

Thanks in advance...

Steve