msrdp persistence through ISA

We have a segment of our terminal server farm published through ISA. Whereas the msrdp persistence (non-default, uses the userid instead of session directory) works internal, it doesn't work through ISA. I think the problem lies in the fact that with native RDP, the userid is provided on initial request, whereas with the ISA, it is not. A login screen is splashed back from the server after the connection has occurred. I'm guessing the F5 is looking for this information in the first packet following the handshake, so in the ISA scenario, all is lost. Is there a feature on the ISA that can require the user to supply credentials up front? I have seen some documentation on the knowledge base indicating the user has some control over this, but I didn't see anything specific to the server. I'm not a windows guy at all, so I could just be searching for the wrong keywords. Any help would be appreciated! Thanks.

 

 

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