Need to assign costs to a pseudo hammock activity

[airduds]

I need to tie a support activity to a change of tasks such that it acts like a hammock - that it's duration mimics that of the work activities. There is a fixed cost per hour associated with the support activity that I would like to be able to show.

Is this something I'm going to have to manage manually?

Primavera P3 3.1 sp2

Thanks for your help