If you completely recoded it, sure. The SCUMMVM GUI is a nightmare beast of horrible code. Another keyboard-ish option is the text wheel system, where you have a wheel that contains ~5, ~6 characters at a time. Either a direction or button press advances, holding R capitalizes, L or Z can form special characters, A selects, B backspaces, C l/r moves within the word. I've found it a bit quicker in most cases, and certainly takes up less screen space.
I want to get it to work, but I'm just not savvy enough. The scummvm forums are of little help. Seems they just made a cryptic port and forgot about it, and now I'll never know if it worked with the N64 keyboard and mouse.
Did anyone ever write up a specification for an N64 keyboard? There should be one for the mouse, but never saw one for any of the keyboards. Similiar story behind most other N64 emus. Just try to track down anything about the MSX one, or the ill-fated SNES9x port, or the GG demo. Huge kudos to HCS for not only making a playable emulator but for acknowledging its existance afterward.