Undercutting your raised carving will cause the stain to accumulate there. If you then take a bit of steel wool to the tops (after it dries), and knock a bit of the stain back, (go slow here) those will be highlighted. If you keep the undercut thin, the varnish will then accumulate in the same undercut and effectively glue it back down.
I also recall a member using a pencil at the base of his raised features prior to staining.
The thing with wood and stains is that the open ends of the cells are going to absorb stain going in both directions, so while you might wish to darken only a portion of the feature, and in only one direction, the stain absorbing is going to go as far as the wood wants to take it, and in all directions it can go (which is why the stripes are dark, and in between them is light).
The idea of a wiping or gel stain is a very good one, though I would like to know the technique for applying / controlling / removing it in the very very small and intricate features that we sometimes carve. Sounds promising though.