Do people distribute their non-free code, which then, somehow bootstraps GPL libraries (from GPL sources)? Would that be compatible with the GPL, or is there a provision against that?

Any project that builds using Maven does that all the time!

(And really it's not simply a question of "non-free" -- there are plenty of open source licenses that are incompatible with the GPL. Is this technically a workaround for the incompatibility between Apache v2 and GPL v2?)

But a non-free villain could bootstrap a build using Maven without even publishing their source at all -- just keep a Maven repository with their binary jars and and a pom.xml that specifies dependencies on a whole bunch of GPL libraries.

Is there a provision against it? I hope so, but I haven't found it yet.

http://wbillingsley.blogspot.com.au/2012/06/does-oracle-v-go...

Presumably, if proprietary code isn't linked with GPL code, it's not a derived work, but two separate works under different licenses. If your situation can tolerate it, you might could write a gplserver running in a separate address space. Or, if it's hardware to hide, video drivers frequently provide a razor-thin kernel driver that does little more than let you mmap the device's I/O space, with all the action sequestered in a proprietary userspace library.

c.f. rlwrap

You're still linking in the free software. If dynamically linking the normal way would be verboten, I can't see why dynamically linking that way would be any different.