20mg test prop sublingually doesn't sound like much at all, you'd probably need like 5 or 6 of them to equal 50mg IM . Also I'm unsure but I assume the longer the ester the less easily it will be absorbed through the skin and mucous membranes, so prop would be even worse than test base sublingually.
I've thought of making them though but they'd be more like 150mg test base per, easiest way would just be to get powder and make them yourself