With a two piece syringe/need like BD; just pull back on the syringe when you are done injecting and unscrew the needle.
Using a insulin needle you can draw up the rest of the testosterone in the syringe by simply pushing the plunger up to where the excess test would spill over and draw it up in the insulin pin.
Do this with each of your two injections and you'll have about 125 to 150 iu's of additional testosterone you can inject SQ between your two injections for that just a little bit extra
Been doing it for years...