linking against -version-info

Hello,

I have a question that may be blindingly stupid, but I've searched the 
libtool manual and the web in vain for the answer.

If I have a libtool library linked with -version-info=c:r:a, how can I 
specify an interface version when linking against that library? That is, 
how can I specify that I want (say) libfoo interface 5?

I'm using autoconf-2.5/automake-1.8 if that makes it any easier.

--
Omer Shenker