One problem with this solution is that a student could enter the same answer for both blanks and get the question "right". Let's suppose the question was something like, "The colors of the US flag are `red`, `white`, and `blue`" and you want students to be able to write in all three colors, but like in the original post, it doesn't matter which order. If red, white, or blue was a possible answer for each blank, then a student could write in "red" for all three and get it "correct", when that would be a mistake. This came up in the context of an exam where it's really important for the students to be able to write in the answers from memory, so drop-downs and word banks would not suffice.
Any ideas?