Two different keys on top and bottom of connected staves?

Hello friends. I am transcribing violin duet exercises which have two violin parts inside one system (like a grand staff, but with two treble clefs instead). I do need these to be attached, so they play together.

Sometimes I need to make one instrument a certain key and the other iinstrument part a different key, but I can't seem to change just one. I understand this would not be common, but I do need it and hiding the key signature itself is of course not much help as I do need a key sig there.

For example,
Violin I: Key of C
Violin II: Key of G

or

Violin I: Key of A
Violin II: Key of D

And I don't seem to be able to just highlight one of the sharps in the key signature to hide it, which would be less ideal of a solution than actually just changing the key, but apparently not possible anyway.

I've been making do with accidentals in the other instrument's part, but I would much rather it look clean, and just in the right key.

Any ideas, friends?

Thanks in advance,
Antoinette