How about giving contributors not employed by Google or Open Handset members
a free Google phone once they have a certain number of patches in the
Android stack.
It is easy to do (just grep some SCM output, or just put "providing proof"
burden on the applicants) and the number of patches needed can be set so
that certain budget limits are not exceeded.
Kernel hackers would certainly be ledgeable and if they bother to apply for
a phone they might actually contribute patches.