Let's say you have collected 5 Precursor Orbs and you want all three Level Selects, copy the file with 5 precursor orbs 3 times into the remaining save slots, and activate Act 1 Level Select in the first file. Then activate Act 2 Level Select in the second. Then activate Act 3 Level Select in the third file, and now you can have all three Level Selects!

Note: This trick can be used for the other secrets also.