Conflict between 1.8.7 and 1.9.3 installations

I've got installations of 1.8.7p334 and 1.9.3p0 in /usr/local. But there's a conflict in the location of one installed lib...

Configure ruby 1.9.3 with:

   ./configure --program-suffix=19

Then 'make install' installs libruby-static.a to:

   /usr/local/lib/libruby-static.a

This conflicts with an existing 1.8.7 installation. The conflict appears in an extension's extconf.rb when calling

   have_func('rb_thread_blocking_region')

which should fail for 1.8.7. (This happens with the eventmachine gem.)

Is there some configure argument that will give libruby-static.a some suffix for the 1.9.3 installation?

Should I use --libdir to keep all of 1.9.3 separate from 1.8.7?

Any other suggestions (other than rvm)?