Scoring eCommerce "tips" - suggestions needed

Ben Smith

In Convio's eCommerce tool, Thirteen utilizes the "Additional Donation" feature that allows user to add any additional donation amount they'd like to their eCommerce transaction. Only a tiny fraction of users actually give an additional amount. I'd like to spice up the call-out for that feature. The field label is simply: "Additional Donation".

Any suggestions for better text that might grab the user's attention and convince them to give an additional gift, but is very brief?