Flipped over and reversed thumbies work well for me. It took a few
minutes to get used to shifting with the "wrong" or opposite hand.
I'd even suggest that the closer the cogs are together, the less
chance there is of misaligning the RD. Another plus (or minus I
maybe) would be that your buddies are much less likely to want to
borrow your bike with the unconventional set up.

Try it.

MW