Sure, no problem. Whether that’ll actually tell you enough about the configuration is another thing. You could even use just about anything to lock the cable to any intermediate gear you wish. I’d suggest the one with the helpful adjustment markings.

Then it might get difficult. Not everything can be MacGyvered at zero cost with a reasonable effort and acceptable results.
One option is to carve a wooden dowel, one end to fit into the bar end, the other to fit the shifter.
without knowing what’s in your parts bin, that’s the lowest cost option I can think of.
Or it might have been the front derailer. Or brake pull. Or flat-mount vs Post Mount calipers.
Or....
Drop bar conversions do hold some traps for the unwary.