processor bus tristate at two places

Hi,

I have my VHDL modules which access the processor bus.
I have one more third party core wher in at also uses the processor bus
, now i have no access to their source code.

Now my doubt is how to go about integrating these two since the
tristaing of the processor bus should happen at only one place.

Any innovative soultion?? OR is it really possible or not.

Regards,
Prav