I have never seen a script for this purpose but for me, what I would do is find a script that will allow you to create images on the fly. There are a few out there for both ASP and PHP. As a matter of fact, depending on your version of PHP, it has functions built into it that will allow you to create images on the fly. You just take the data from the customer (ie: Font Choice, Text, Color, etc) and format it properly using the built in functions.
VistaPrint.com is a wonderful example of a live site utilizing ASPX for this purpose.
Sorry I couldn't be of any more help.