I think when an action takes an object as a parameter it's not picky what kind of object.
Form objects actually float above the game canvas so they don't draw. I think the only workaround for that is to somehow draw the form controls on the canvas. You can do that by setting css opacity to 0 and doing the drawing by other means. However, there seems to be quite a bit of nuance to draw the same.
Here's a test of hiding the inputbox form and displaying it by other means. Needs work when more text is displayed, but it may give ideas.
dropbox.com/s/5xygyt0uo5zyz96/hidden_input_form.capx
A simple solution would be to limit the number of characters?