Take a look at the actions performed in the Users list or any other list in the CMSDesk or CMSSiteManager that utilize a UniGrid. You'll find most of them redirect to a aspx page that opens in a modal window. You can perform this same type of action and simply use a generic "form" but the end result is the action performed is defined in the XML file for the UniGrid.
I've created a
webpart in the Marketplace that does this same type of functionality with custom tables. You might check that out and download the code to see how I populate the form from the grid actions.