I smell a bad idea for multiple reasons.

#1, 100% H2O2 Will pretty much react badly with any impurity. (they use it for rockets for a reason)
#2, if you have ever frozen low percentage alcohol (beer), you know you don't end up with a nice layer of alcohol and a nice layer of water. You get a slush. Not sure how that helps you get 100% h2o2.
#3, it would be much cheaper in the end to start off at 35% Peroxide, but it would also be much more dangerous.

-edit-

#4, low cost 3% peroxide is often impure and has chemical additives to stabilize it (another reason to use food grade 35%)