Remap Top-Row Number Keys I've tried Ukulele and KeyRemap4MacBook. Neither does what I need to do.

I want to map the top-row 4 key and the top-row 8 key to SHIFT. So that, for example, when I press 4 + g it types a capital G.

Hitting the shift key with my pinkie is aggravating my carpal tunnel. On my windows machine I just remapped 4 and 8 to shift and I use a keypad if I need numbers. Savior for my hands.
Ukelele should be able to kind of do this by making 4 a "deadkey" that generates the uppercase letter for any key typed after it, unless there is a limit on the number of keys you can have in such a sequence.  (Just like alt + e is a deadkey that generates acute accented versions of any vowel typed after it)

Of course this is not exactly like Shift, because you can't hold it down, you have let 4 go before you hit the next letter.