After seeing your post I did some digging and it looks like you may be able to do this.
I went to Micromatic.com and there is a pretty big difference in the main assembly for sanke connectors that are for hand pumps and sanke connectors for CO2.
Below is the hand-pump type and the CO2 type. Note the difference in body style.
HAND PUMP - Air goes in the top, beer comes out the side.
CO2 - Gas goes in the side, beer goes out the top.
That being said, if you can find a barb fitting that has the same male thread as the hand pump that attaches to the top of the hand-pump sanke, then you could replace the hand pump with that barbed fitting and connect a gas line to it.
I'm not sure what the threading size is for the hand pump, but I can take one of my hand pumps to work tomorrow and measure it with some thread gauges and let you know. This may be worthless though, since there is no way to tell if your connector has the same threads. Mine is a Micromatioc brand, if yours is different you will need to figure out the thread size on your own. To do that take the pump or the sanke connector to your local hardware store and they should have a little display bench with different size threaded adapters and will be able to tell you the size and thread type. Just take the parts in and tell the guy, "What size thread is this"? I'm pretty sure you will be able to find a stainless barb fitting on McMaster Carr that will work for cheap. Reply with the thread size and the ID of your gas line tube when you find out and I can help you find the right fitting.
Another option would be to just buy a new hand-pump from micromatic.
LINK
Cheers!
School Master