libtool and --enable-new-dtags

[Poor Yorick]

When building software which doesn't use libtool, but does use autoconf, adding
"-Wl,-rpath,/path/to/lib -Wl,--enable-new-dtags" is usually sufficient to end
up with a shared object that has a RUNPATH value.  I haven't yet figured out a
good consistent way to do this with libtool.  A solution that doesn't involve
modifying package Makefiles or autoconf files would be preferred.  Is there a
nice standard way to get libtool-enabled packages to build like this?