Powershell uses the @ for "splatting" thus it can no longer be used for argument lists. Error below "The splatting operator '@' cannot be used to reference variables in an expression. '@xmlp' can be used only as an argument to a command. To reference" Not sure what to do about it, but thought this would be best place for it.
Can you use this: http://stackoverflow.com/a/5571703 ?
The workaround is probably accurate. I no longer use this approach to know if it would work in my use case.