ksh has a method for communicating with a coprocess which we
used a lot when I was at IBM.  It works a lot like expect
except that it's a lot more sensitive to carriage control
It will do what you want I'm fairly sure.  I don't have
ksh anymore so I can't send you working code but it was 
something like:

exec |<some program>
read -up foo
write -up $bar

YMMV, man ksh is your friend.

pjr