Add Feature to selectively insert letters - not just the leftmost ones

[erdnuesse]

Is your feature request related to a problem? Please describe.
I'm always frustrated when [...] I want to put letters where I know they belong, without starting left.

Describe the solution you'd like
Being able to select and enter Letters 1-5 separately, without being forced to enter a whole line up to the letter I want

Describe alternatives you've considered
Using X-es or another letter just as placeholder is a hacky workaround

Additional context
Optimal:
Use the mouse or arrow keys to select a position, press the letter, and have it appear there.
Helps people think, and I would guess that's how many ppl. play the game.