How to check if a resource plan is checked out in the PSI.

I've tried searching before but I couldn't find a clear cut way of telling if a resource plan is checked out or not.

One thing I found is the ReadResourcePlanStatus method but this does not tell you if a plan is checked out or not.

It only has states Absent, Working (in a draft state) and Published (in a published state).

Looking at SQL Server, I found a column called RESPLAN_CHECKOUTBY in dbo.MSP_RESOURCE_PLANS and I think this is perfect for what I need. If it is null then that means its checked in and if not then it is checked out.

What is the easiest way of accessing this through the Resource Plan service?