Would it be possible that the wheels could be built in a more-trusted / hardened environment? Having a binary blob isn't as serious when it comes from a trusted source. Almost all Debian/etc linux distributions have this feature (binary-downloading package manager).

The hardening could mitigate on-compilation hacking.

Obviously, this leaves "compile in the backdoor and wait for the user to fall into it" but at least this isn't an issue of compiling on the user's computer and it isn't a issue of binary blobs. And possibly there's a greater chance of detection if actual source code has to be available to compile.