Absence approval delegation using vacation rules.

Summary:

We have a requirement that the client doesn't want the approval to go to higher-level line managers instead, it should be redirected to their assistants.

Content (required):

We have approvals and escalation configured where when Employee raises absence approval goes to Line Manager, if not approved within 2 weeks then escalated further. 

There are about 20 users for whom we will need to write a separate rule, but we don't want the person to whom the approval is getting delegated to have a lot of access, so can we create a rule based on only one Absence Type?

Please suggest if you've faced similar requirements.