I have an application that I need to use a PowerShell command for its detection that the cmdlet isn't available until Windows Management Framework 4 but if I add WMF4 as a dependency to this application the Windows 7 clients, not at WMF4, are not able to see the application because the detection method fails.  I do not have the ability to deploy WMF4 to all clients and I need to deploy my application as 'available' to all clients.  

How can I get around this catch 22?  

Don't use powershell but vbs as the detection script?

Sigh.  ConfigMgr needs to allow "post dependencies" which would run after the primary app installs, this would solve all these weird situations.

I concur. Pre- and post actions would be most helpful. To my knowledge these have been submitted in the past as design change requests but nothing is stopping you from adding this to connect or uservoice.