Dual Purchase Approvals

Dual Purchase Approvals

I'm not sure if I'm overlooking how to do this or if this should be a feature request. I need to have a user that currently has a purchase level of say $10000 with a higher amount that can only be jointly approved if the CIO is out. 

Example:

Sam currently has an approval level of $10k.
Sandra doesn't have a current level.
And Tom has a level of $1m.

If Tom is out (for whatever reason) only together can Sam and Sandra approve Tom's amount. Otherwise, Sam can only approve 10k and Sandra nil.

Thank you for your help!