Can I change the RTC Planned For attribute to use a custom Iteration attribute?

Hi

We want to use two Planning attributes for an RTC 5.0 work item, one to track the high-level target release e.g. "Nov Release" (linked to UrbanCode Release 6.1.0 releases), and another for the target iteration (linked to the RTC iterations).

I've renamed the default "Planned For" attribute to "Release Planned For" to indicate the high-level target release, because it appears that UCR only works with the default attribute.

I've also created a new custom attribute "Iteration Planned For" of type Iteration, and I wish to use as the iteration planning attribute.
Unfortunately I cannot see any way to change which attribute RTC uses as the Iteration Planning attribute.

Is the above achievable?

Regards,
Sudheer