'Instance-independent' container

[Huba H]

Hi WUG Members,
We are impleneting approval flows based on multiple cost centers (1 cost
center = 1 department) based on the CC-s entered for the transactions (PO,
Preq, etc.).
The approval flows run parallel for each Cost Center. The main WF spawns the
approval (sub)flows in a dynamic parallel session manner, the number of
branches running parallel equals the number of Cost Centers within the
transaction.
In order to avoid sending the same WI to the same approver, I maintain a
list of approvers in the container, and assign it to the 'excluded agents'
(it is necessary , because multiple Cost Centers roll-up to the same level
higher in the hierarchy (director, VP) ). My problem is that -of course- the
subworkflows do not see each other's approval list, which means, when they
roll-up to the higher level there is no way to tell whether another branch
(from other CC) already sent out the approval WI to this particular director
or VP.
Is there a way to define 'global' or 'instance-independent' container
variables (in this case the approval list) that is visible from each sub
workflow instance running parallel to each other that belong to the same
main WF ? I'd rather shy away of using custom db tables for this purpose...
Your help is highly appraciated,
Thanks very much,
Huba Horompoly