He could add some DMSO or some other skin penetrating agents to it and it might increase the absorption through the skin barrier. The molecular weight of testosterone base is 288, well below the ~350 threshold for not being absorbable, but still a large molecule.
I don't know what the other ingredients in the cream are to say whether or not the pharmacutical company that produces it has taken maximum advantage of getting it through the skin barrier. @
YoungThor if you could list the other ingredients in the formula (check rxlist.com, it should have them if it's not inside the pamplet in the box it comes with) that might be helpful. This is just a theory, so I couldn't guarantee it would help, but I can give you a list of some other ingredients to add and sort of cook it up into a better "homebrew" transdermal test it might help you get more bang for your buck.