I don't mean adding streaming to S3 ruby lib, everyone's done that by now 

.  As you sort of allude, I think you really do need to add some code to net/http to get the *capability* of streaming at all.  And I don't know how easy it is to backport.
I am not even going to consider anything pre-1.8.4 as supported, since that was the minimum version I wrote the original code to!  If someone wants to back-port, I will be happy to maintain a "compatibility" release here.
As background: is mac not capable of easily running anything less archaic than .2?