I spoke with Susan Bulgawicz again today.  She relates the following points:

Gensler has been subcontracted to do interior space planning and design for 
the new building generally
While our work is probably in addition to that already agreed (and will 
therefore be billed to us) it should be covered by an amendment to the 
existing agreement rather than a new, separate agreement
Bill Donovan feels that the design and space planning work should be done as 
near in time as possible to the actual construction work to avoid having to 
redo the work (and pay twice) to take into account new factors not apparent 
earlier (e.g. organizational and technology changes)
Bill's view is that we are 3 to 6 months premature at this point in doing 
this work for the legal department

Susan suggested that you might want to call Bill to discuss this and talk 
about how you want to move forward.