It is actually quite simple to do bleach bypass with a kit that supplies BLIX: these kits supply two bottles for mixing BLIX, and if you look carefully you will see that one looks deep red like Ammonium Ferric EDTA while the other one looks slight yellowish like Ammonium Thiosulfate. Just leave out the deep red liquid part and you should have a fixer.

If you want to use your own fixer, make sure it is neutral, PhotoEngineer gave us recommended pH between 6.3 and 6.7 on multiple occasions.