Note that I'm not referring to using hard-coded coordinates. It's important to retrieve the X and Y values at runtime. And as Nilesh mentioned, it's important to have the app maximized as well. In general, what it sounds like you're trying to do is not one of Blue Prism's strong points. It can do a lot of things and what you're going for might be possible, but you should expect to have some serious knowledge of Blue Prism and doing things like this already. I don't mean to suggest you don't have that capability; but if this is the first time you're attempting something like this, I would get the most experienced developer you can find to help you troubleshoot and come up with ideas on a call with screensharing.
My original suggestion still stands though, I think, and that is to use whatever spy modes and elements you need to in order to identify the X and Y coordinates on the screen of the elements that you need to work with, and then try Drag and Drop with those coordinates. I just don't see this working any other way with the features I'm aware of in Blue Prism. I think it'd be a great enhancement request as well if you can figure out the scope of changes required in Blue Prism. I haven't found very many business processes that require drag and drop personally so I'd probably be tearing my hair out if I were in your position. =)
------------------------------
Dave Morris
Cano Ai
Atlanta, GA
------------------------------
Dave Morris, 3Ci at Southern Company