Unfortunately, the short answer is no. Here's a link to a related thread with additional additional details from the Sling Pro section. Disregard references to the HD Connect dongle, that stuff is built into the Pro HD:
It comes down to the HDCP copy protection scheme built into the HDMI spec. The CableCo's don't have to enable that "feature." But if they do, I'm unaware of any reasonable way around this except to discontinue using HDMI and go with component.
Hope this helps,