I posted just such a patch exactly 3 years ago today (coincidentally) -
here's the thread:
http://thread.gmane.org/gmane.comp.gnu.libtool.general/8339/focus=8345
Back then Ralf said "Olly's solution should not be forgotten, though", but
it seems it has been.
I've been using this code in Xapian to override libtool's version for a
couple of years now, with no reported problems.
The only downside is that it can be quite slow to get the list from
ldconfig (I haven't investigated why or if this could be improved - it's
interesting that it always seems quick if run a second time which suggests
either a cache issue, or that there's a cached value being updated), but
the speed of the current approach seems greatly outweighed by the wrong
answers it gives.
As I said in the original thread, if the patch is wanted I'm happy to
update it for current libtool and write a ChangeLog entry.