Is there any way to add a variable in a field that is hidden (Twitter example)

Is there any way to add a variable in a field that is hidden (Twitter example)

I'd like to create a field for my clients Twitter name.

Usually that name is something like this without the @ sign:  @TwitterName

What I'd like to do, is set up the field so that all I have to do is enter their twitter "TwitterName", and have ZohoCRM insert the rest of the link hidden, so that when I view the record and click on the name, it goes to http://www.twitter.com/TwitterName


How can I do that?  Is it a formula?