Hook to add a processing animation

[aeu]

Hi - I'm not sure if this is actually a missing feature or not, but I can't find anything in the documentation.

Currently when the user hits submit on payment there's a delay from the time they hit submit and the order success page. We would like to add to our store some sort of indication that the payment processing is happening. Is there a away to attach a callback to the submit so we can give the user an indication that processing is happening?

Thanks!