Nested OL digit.digit style list for IE7 (and below) - Javascript solution?

Question

This was hinted at in another post, but I need some assistance with displaying a list like this in IE7

1. 
   a. 
   b. 
         1.0 
         2.0 
           2.1 
2.

I think I am limited to JavaScript because of IE7's lack of CSS :before support. For example, this does not work

OL { counter-reset: item }
LI { display: block }
LI:before { content: counters(item, ".") " "; counter-increment: item }

Any pointers?