I was gunna say just do:
BRLFlushKeys()=FlushKeys
FlushKeys()=MyFlushKeyFunction
then
BRLFlushKeys() 'use the original
FlushKeys() 'use yours
BRLFlushKeys()=FlushKeys
FlushKeys()=MyFlushKeyFunction
then
BRLFlushKeys() 'use the original
FlushKeys() 'use yours