SOURCE_PATH in ZFD app distribution...

I'm struggling to understand how to best specify and use SOURCE_PATH when
distributing apps from a single distributor to subscribers that have a
different volume and folder structure... (legacy servers)

The apps are predominantly MSI, so we need to bear in mind that the
distribution just hoovers up everything under the path specified in
Common->Sources folder.

Ideally i'd like to set the SOURCE_PATH on the individual app object and
then use some 'variablisation' (!?!) on the subscribers to sort the paths
out. However, I can only get the distributor to gather if the SOURCE_PATH
variable is set at the TED policy within the service location package that
is specified on the container above the distributor object... (If I don't,
I just get an error in the TED.LOG:

' the source path %SOURCE_PATH% is invalid. Make sure the "%SO" variable
value is defined in the Tiered Electronic Distribution policy, and that the
policy is associated with the Distributor objects parent container.'

This means I have to set the SOURCE_PATH in that policy for the Distributor
and then specidy specific SOURCE_PATH variables on each subscriber
object... The golden app objects then reference this 'global variable'
with an appended path in the common sources e.g. %SOURCE_PATH%\acrobat

This works... however my concern is having to specify a single SOURCE_PATH
variable that is at the 'root' of all the applications.... If someone gets
trigger happy with an app distribution, they could inadvertently specify
just %SOURCE_PATH% and end up hoovering up all files and folders in that
structure..... I'm sure this would probably kill most of the subscribers
and wan links....!

There must be a better way?! Any suggestions welcome!
Many thanks

David
BTW ZFS/ZFD 6.5SP2!