I agree that water is good to use. I have also used vodka as it evaporates quickly and leaves no taste behind.
Side note if you actually do want a recipe for gumpaste glue: I did a gumpaste flower class back in January and we made gumpaste glue by putting a small ball in a bit of water. Seal it in the container and allow it to sit in the fridge overnight. You only need a smidgen of this to adhere pieces of gumpaste together. The instructor said it will keep in the fridge for quite some time. She says you know to throw it away and start over when it starts to smell funky.
Here's tylose from Country Kitchens if you still want to use your recipe for gum glue: http://www.countrykitchensa.com/catalog/product.aspx?T=1&productId=619070
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