connect PPTP Server behind a GRE tunnel

Hello everyone. I’m not sure which forum should I ask in, so I post it here.

Here is the scenario I want to build.

Cx, the internet client customers using pc or android devices;

A, My public service ROS

Bx, some PPTP VPN servers which I want them to serve for Cx.

A & Bx has GRE connected like this: A (1.1.1.1 --gre-- 1.1.1.2) Bx

Cx make the pptp client connecting to A, then A transfer the request to Bx and Cx will connected with Bx by PPTP. Bx will alloc a internal IP (like 10.12.13.x) to Cx.

Can this happen?

Thanks for your time.