I was just doing some silk dyeing the other week--instead of discharging out the white, you could try using something called Batik EZ. It's a fabric resist, just like people use in the wax-batik method, but way easier!
You paint it on your fabric first where you want areas to be white, and then you dye it (either paint the dye on or dip it). The resist washes out in water--pretty cool, huh? Here's a link to how to use the Batik EZ: [link]
I've also heard you can use Elmer's blue school glue gel.
Here's a link to the gel glue method:
Let me know how that works for you!