BOOTP used accross WAN link

We are having a issue with using BOOTP accross the WAN. Here is our situation, we are trying to image some thin clients at a remote site that need to connect back to our main site over a 512 K Frame-relay connection. On bootup the thin client tries to connect back to a Rapport server at the main site using bootp but cannot connect to it. The DHCP server dishes out ip addresses back fine however. This setup works fine when we test it over different subnets but off the same Catalyst switch. So is there something I'm missing in the way bootp acts when crossing multiple routers?
We also ran a sniff on the udp traffic coming in and out of the Rapport server and found that when we boot a Thin Client that is connected into our core switch (different Subnet) it reports to the Rapport server with no problems and in the capture of the packets we see a Discovery, Offer, Request, and Accept. But on the capture of the Thin client booting from the remote site we see only a Discovery.

Here is the configuration scheme:

Client Site router:
 ethernet0/0
   ip address xxx.xxx.xxx.xxx
   ip helper-address xxx.xxx.xxx.xxx  <== Rapport Server address. This is different from DHCP server
   ip helper-address xxx.xxx.xxx.xxx  <== DHCP server address

Any ideas would be greatly appreciated!