Option to duplicate + comment #84

Very often I like to duplicate a block of code and comment out a copy.

For example,

for i in range(2, 20:
     print(i)

# for i in range(2, 20:
#     print(i)
for i in range(2, 20:
     print(i)

Right now, I have to repeat a motion twice -- once to yank and once to comment out. And then of course I have to hit p to paste in the duplicate. It gets more complicated if I have to avoid clobbering my default register.

It would be nice to have this all rolled into one motion (that takes care of saving/restoring the registers).
Eg., gC" (or gyetc.) will behave just likegc`` but will paste a copy of the uncommented code next to the commented one.

Is it possible to support this?