my advice - don't do it! well, not as a real test anyway.

you will get 2 lines and the test line will be lighter than the control line, just like early HPT's look. But this is just the leftover LH in your system. I *think* (not sure) in order for it to work as a HPT the line has to be like it is for the OPK, as dark or darker than the control to be considered positive.
But I *think* (not sure) you'd get a response earlier with an early HPT than you would using an OPK.