Is subcutaneous injection really that untargeted? And does the highly interested patient have the background to know how to inject it properly, if there really is a way to target it?

Further, consider insulin. It's typically administered as an aqueous solution injected subcutaneously, and it's absorbed quickly and systemically, with local effects in the near-zero range.

It's possible to make an aqueous solution for SC injection that might have some degree of local efficacy, if it's injected near a target site. This, however, would involve tinkering with the PH of the solution to induce drug precipitation, post-injection, near the injection site. It's complicated, and not the sort of thing that gray market research chemists do.

Liposomal delivery might even work for far larger peptides and proteins. For e.g., there has been quite a lot of research into liposomal insulin: https://pubmed.ncbi.nlm.nih.gov/2226109 and others.

The thing about BPC-157 in particular is that it has, in principle, pretty good oral bioavailability, and it's not clear that it would benefit from liposomal delivery. You'd probably want to run a comparative analysis -- liposomal suspension vs. plain aqueous solution -- which would be expensive no matter how you go about it.

We are explicitly trained in the ED that oral steroids have been proven equivalently effective and much cheaper than parenteral administration, and so should be preferred for patients that can take them by mouth.