Not possible out the box I believe. I know there was a request to have the Escalation time changed after it was started (which would help you) but not sure about the ETA of that.
A simple workaround I can think of is to have another Client after the initial one, lets call it Client All and Client One. Client All has no escalations and a dummy page that just finishes the task (synchronously) and then redirects to Client One. Client One has the actual Escalation set and since the user is redirected they won't really know that they have visited 2 pages.
Not the cleanest solution but it should work. Issues I foresee however:
- You will have "duplicate" client events
- Housekeeping will be tougher when working with multiple destinations.
- If you send email notifications, it will still point to Client All after the initial hit. The page should be able to handle this though, check if current item exist, if not, find the Client One Worklist item for the same proc inst (id in Serial Number of course) and redirect.