Hi Bob, we did indeed add this feature in 8.100. It will be very rarely used, and isn't a benefit unless a customer has this specific need, however it is in there.
Sascha, you can configure this by first going to the profiles section and clicking on the new "parent proxies" tab. From there, the "order" of them can be defined using the http-->advanced section if needed, but 99% of the users who need this feature will just do it in the profile itself.
