Well I guess you could use something like that:
http://notimpossiblelabs.com/eyewriter
with some software modification (pure speculation as I haven't even checked the code) you could use eye movement and blinking to simulate mouse input and with on screen keyboard you should be able to write your password somewhat securely
http://www.ted.com/talks/mick_ebeling_the_invention_that_unl...also shouldn't be expensive to build...
[edit] link to the github repo
the software can be found here https://github.com/eyewriter/