If you find out, let me know! I feel like all the styles could use such a thing, on account of the default mobile style pushing all the modules down below every single entry on your page.

It may be possible to do this using an S2 layer, at any rate? If you look at my journal (which I accidentally reverted to a previous customization, oops) it currently has things like a (broken) Tumblr share link down beneath each entry. There should be an entry on this community where I discussed this and asked for advice.