[cybio]

yes, but you have to do it on your own/you have to add the html-code directly (you can use all possibilities of floatbox/floatbox plus is just a "helper" to use floatbox within wordpress)

if you really need a "helper" (i.e. a small popup in the editor of wordpress with some options) to add a link using floatbox (or something else) and you can't wait, you can contact me and for a small donation it is possible to get the function asap (otherwise you have to wait/most feature request will be implemented, but i can't say when it will be done).