In terms of C++, I picture the MFC IDE you mentioned to be somewhat similar to VB Visual Studio. I Imagine there are functions for each window control's event like in Visual Basic. So all I would have to do is reference the values in the textboxes, append them with spaces, and then set the clipboard string to them. So I would add a control (like a button) and then define its event function (button.click) to do this.
It's kind of like that, except that I can't promise double-clicking the control on the form designer will add the code in the right place and all of that... you might have to try to follow the example of neighboring code. But for what you're trying to do, it shouldn't be brain surgery at least - you can probably just stick to the UI layer if you want to.
You probably will need to reference MSDN's MFC documentation regularly, though, and you also have to get DLE to build. Which might not be ridiculously complicated, but if you're using a more recent version of VS there might be some tweaks to do - I recall 2013 gave me a few complaints about the use of deprecated ASCII functions, but there was some way to suppress that.
I've occasionally done mathematical calculations for building levels, though some of them I've tried to replace the need to. I recall in FV-24B I was using trig to attempt to make the central platform with the reactor a perfect hexadecagon; in Anthology I did some manual UV projection/scaling to mimic D3's terrain texture alignment (which I repeated in one of the Descent Vignettes levels, although I used a programmatic projector to do it there, which is now built into DLE's texture projection tab); and in TEW for Pinhead, I wrote a little utility in .NET to more quickly calculate the co-ordinates I needed to move a point to to get it onto a sphere, which sounds awfully similar to what you're doing. That was one-way, though - I copied the numbers and pasted into DLE - not vice-versa.