gpgme passphrase help

[Hans Alves]

Hello folks,

I am trying to write a GPG plugin for Geany, using GPGME. So far, i got 
the encryption working, but, when the user does not select any 
recipients, i want the plugin to use a symmetric cipher. The problem 
is that i can't seem to figure out how to get the passphrase 
callback working (safely). From the GPGME manual I understood that it
would be better to make use of gpg-agent instead of writing my own 
passphrase callback. But, I can't find how to get GPGME to use 
gpg-agent.
Another option would be to use pin-entry directly, but than i would need
a way to redirect pinentry's output to the provided file descriptor on 
Windows (I really want it to work cross-platform, even though i don't 
use Windows myself, and as far as I know windows doesn't implement
dup(2))

Any ideas on what i should do?

Thanks in advance,
Hans