change IP-Address for Indy/UDP

Hi there,

I hope my problem is not too trivial ..
Could anyone tell me how to assign a special IP-Address to the
UDP-Client and -Server of Indy?

Cause of my home-network, Ive got 2 IP-Adresses on my PC,
that means for private use and the one my provider
applies to me, when I dial in.
But I want to use explicitly the last one. I found methods to get
the addresses of my system, but not how to tell Indy, which of
them to use. The port-number is easy, but the IP-address?

many Thanks