They used to support this feature up until the Slingbox Pro-HD but then they removed it from the 350/500 onwards.
There were numerous requests at the time of the 350/500 release a couple of years ago for the feature to be brought back as it was very helpful for some peipke to be able to manually choose the port number, but they ignored them all so I wouldn't hold out much hope it's in their plans.
They did move my original post on the port setting to the enginners forum as a enhancment request. Here's to hoping! This is a major feature for a streaming device... you absolutely need to be able to set the port it uses or you lose complete control of the device.
I just can't believe they left this out again.
The M1 works great but I sure would like to use it remotely! LOL!! ;-)