There are two main ways to make a yeast GF, the first is isolation then inoculation, the second is a dilution solution.
We will start with the more complicated isolation and inoculation method. First you will need to pour GF agar plates, I would follow dkershner's method for making and canning starter wort, http://brew.dkershner.com/2010/step-...-starter-wort/
with slight modification. 1st make sure the wort is GF, then add 10g/L agar (which can be found at a health food store) proceed with sterilization, but only fill the mason jars 1/4 of the way full (smaller mason jars work best). Finally when the jars are cooling set them at an angle so the agar hardens in a slant. You have just poured your first Media Slants.
Now comes the isolation portion, first you need a loop, commonly that is a metal loop that will pick up a small amount of media held in place via surface tension. Practically anything will work here, and if a loop is unavailable a metal fork with a wooden handle will work in a pinch. The goal now is to sterilize that fork or loop, I suggest a propane torch and heat the whole loop until the metal gets red hot.
Now that your loop is sterile, let it cool, then touch the loop to the yeast, to pick up a small amount of yeast and media. Now very lightly streak the loop onto your hardened GF agar, we are not trying for isolation here so I will not get into single colony isolation. close up the mason jar and incubate until colonies can be seen, you have now started your own Yeast collection. Now you simply inoculate your GF starter cultures using your loop and a small amount of yeast colony.
The second method of making a yeast GF, is the dilution solution. I would like to note that the standard for GF is 10ppm, and actually most liquid yeast is only 2ppm. This 2ppm can still be too high for people who are very sensitive to gluten, what we want to do is dilute this 2ppm (parts per million) even more.
Essentially you want to add a very small amount of liquid yeast culture to GF starter wort, if you diluted 1ml into 999ml you have just diluted your gluten to 2ppb (parts per billion) a 1:1000 dilution. Now let it grow up and you are ready to inoculate.
If 1Liter starters are unavailable to you, or you want even less gluten in your starter, take a small amount of this starter after it has grown up overnight, and dilute it again into another 999ml you now have gluten in 2ppt (parts per trillion) which is undetectable by the best of scientific equipment.
Congratulations you have GF yeast and a little hands on experience with sterile technique