You probably need to make a few forms in the Mendix modeller which you will be using for the iPad or blackberry. Create a new form specially designed for iPad users. e.g. "iPadfrm" Second: link iPad users to these forms by e.g. using javascript to determine browser type and redirect to your new forms.

Example javascript: determine browser and add an action to it

This is what I would try but haven't tested it! Hope this helps.