I don't believe this can be done and it is a real pain. Each form is separate so if you hide one button the data entered into those fields will not be submitted by hitting the button in the other form. I did find this on combining two forms into one but I don't know if it works, it's over my head, and I haven't had a need to try. http://community.marketo.com/MarketoArticle?id=kA050000000KysGCAS
David