Adding a snorkel valve is possible, but shouldn't really be necessary. The modellers in Europe use a snorkel valve because they are running high pressure systems and thus pumping with piston type compressors which don't like ingesting water, unlike the low pressure diaphragm types used in the snort system.
You should be able to modify your existing pump without too much difficulty.
The pumps that have only one nipple tend to have the intake port as a simple hole in the side of the pump housing, you can usually locate that fairly easily by eye. Confirm it by powering up the pump and letting it blow air bubbles into a glass of water. Capping the intake port with your finger should stop the bubbles!
Once you know where the port is, scuff up the area with some abrasive, locate a piece of metal tubing (copper brass etc.) and do the same to that and epoxy (24 hour cure variety) it to the body. Then just connect your intake hose up to your snort mast.