OK,
I understand the requirement, but I doubt many people would use it because
it essentially requires a duplicate copy of your used disk space on each
client that is involved.  Run this select.  It will give you an answer in MB
of the space required to do what you are asking.  You can add where or group
by clauses.

select sum(capacity*pct_util/100) from filespaces

I would bet you have no business case for this as you have asked for it.
And, I would bet more likely than not it is the deleted file (most recent
inactive file) that needs to be recovered.

It would be very difficult to garner any support from Tivoli for this
requirement unless I am missing something.