You can do this using the send hotkey activity and pasting it from the clipboard.
When you’re at the point where you want a screenshot, take a screenshot using the print screen button (see thread here on how to do that How can i press PrtScr (print screen) button through robot?)
Then in an excel activity scope use select range to select the cell you want to be the upper-left corner of the screenshot. Then use send hotkey ctrl+v to paste it into excel