You can freeze kefir, but some of the probiotics and good yeasts may not survive. If I needed to stock up on them, I would just buy 2 or 3 and keep them in the fridge and let them get more sour. That said, frozen kefir is still better than no kefir, and I've turned kefir into yummy pops before. Which reminds me, kefir makes good sherbet. If you have an ice cream maker, just substitute kefir for water in a sherbet recipe. You may have to adjust the recipe to use a bit more sugar and less sour fruit since the kefir will add sourness.
Kefir can be pretty sour and still be good in smoothies. You just blend a cup or two with a handful of strawberries, a ripe banana, a tablespoon of honey, and a splash of vanilla. When I want kefir pops, I just pour the smoothie into pop molds.
Other than that, I use it to soak oatmeal in the baked oatmeal recipe, or granola recipe. I also add it to muffins or use it in place of sour cream in cake recipes.
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