1999 TRX 250 Recon — gear indicator addition?

Have a 1999 TRX250 Recon (manual shift) my wife uses it and she has trouble keeping track of what gear she is in. Is there a way to add a gear indicator similar to that on the late model ES bikes? See image attached for reference.

I don’t want to try to put ES on it but am thinking that a gear indicator panel would help her to enjoy the trail a bit more.

Attached Thumbnails

1999 TRX 250 Recon -- gear indicator addition?-gear-indicator-panel-es-model.jpg