I mean to place 2 Text Boxes Fields Next to the [+] and when you press the [+] that the Code reads the Numbers on the 2 Text Boxes, and if the Number is Different than 0 and Bigger than certain Value (width=638 and height=515 in your code), then take those Numbers and use them to increase the size of the Object; if a Text Field is Empty then Use the Default Value (width=638 and height=515 in your code).
And of course that the Use of the Code of the Boxes don't cause any SQL Injection Problem as you mention.
It'd be Nice to Offer that Extra Option.
My Best Regards.