Issue using posts_nav_link and display:block

So posts_nav_link usually returns links sending you to the next post and previous post, together. What I’m trying to do is split it into JUST a link to the next post, and JUST a link to the previous post.

I accomplished this by setting null values in the appropriate areas.

Everything works fine until I put it into an ul that has display:block; for links. What ends up happening is the null value being returned is still generating a link (albeit a blank one).

It’s hard for me to explain, so just check out http://erolcomic.com/wordpress/?paged=2

What I’m talking about occurs on all pages except the first post and last post.

Try browsing around using the Next and Previous buttons. You’ll see what I’m talking about.

Is there any way to return JUST a link to the previous or next entry, without trying to abuse posts_nav_link?

I have a very limited understanding of php (read: none), so your help is appreciated.