Planner-list Fixed duration, partial time allocation

[Mike Hoolehan <mike sycamore us>]

I would like to set a task to be a fixed duration with multiple 
resources supporting at unequal units.  HOwever, if I set a fixed 
duration task, I cannot edit the "Units" field.  Instead, all resource 
units are allocated equally among the checked resources.

If it helps, I want to specify a software beta period lasting two weeks. 
 There will be only 40 actual working hours during this period, 
however.  Of these 40 hours, I want Tester working 30 hours and 
Developer working 10 hours.

Is it possible to reflect this situation in Planner?

Regards,
Mike