Yes we have created several project approvals for our business case all dependent on the total value and impact of the project.
The way we set-up the approval process to trigger is a little odd (as explained to me it is how the Business Case approval process ties to the project status overall), but it works for us.
Once you create a custom Project Approval process (a sample of one of ours is attached here), you add it to your project or template if you use those. When our Business Analyst completes the business case, they "submit" for approval and also "approve" the business case in the same step after refreshing their screen. Once they have done this, the overall project approval picks up on the project status of being "approved" and sets the process in motion and the project is in a project status of "approved-pending approval" while waiting.
It sounds confusing, but it works for us. Let me know if you need further clarification.