As provided in the FutureQuest Terms of Service:
Circumvention of Fees: The circumvention of fees by the engineering of a method that emulates a service or value added service established or offered by FutureQuest, such as but not limited to, the IRM/IRO functionality is strictly prohibited, unless otherwise explicitly stated or expressed by FutureQuest.
However, if you are wanting a subdomain (such as forums.yourdomain.com - where "yourdomain.com" is the domain name of your Full Package), you would not need to register another domain name. The Service Fee associated with this from FutureQuest would be a one-time $25.00 Service Fee. This would be considered a DS-IR.
If you want an IRM or IRO, on the other hand, a domain name will need to be registered with a domain registrar. The one-time Service Fee from FutureQuest to set up the IR would be $25.00.
More information about DS-IRs and IRs can be found here:
Hope this helps to clarify your options,