Chef and Windows - Group Membership Provider

So I need to add a domain user to the local machines administrators group.  Luckily, or so I thought, I could simply use Chef's group provider to do this.

I wrote the step in my cookbook as follows:

This works great the first time, but will fail after that with the following error:
ArgumentError: The specified account name is already a member of the group.

A quick search, and you'll find that this is a known issue, open since end of March.

So until Windows support becomes a priority, we are stuck with a workaround.  We have some options, WMI, .Net, Ruby, or Net.exe calls.

I am sure there is a better way, but I went with the following: