Bypassing shared_buffers

Hello,

There is often a need to test particular queries executed in the worst-case
scenario, i.e. right after a server restart or with no or minimal amount of
data in shared buffers. In Postgres it's currently hard to achieve (other
than to restart the server completely to run a single query, which is not
practical). Is there a simple way to introduce a GUC variable that makes
queries bypass shared_buffers and always read from storage? It would make
testing like that orders of magnitude simpler. I mean, are there serious
technical obstacles or any other objections to that idea in principle?

Thanks,
-Vladimir Churyukin