I was also interested in more ads on the sidebar but was unsuccessful at duplicating the widget so what I ended up doing was to put multiple ad code in the single form field.  Seemed to work just fine.  Pretty much a bandaid, yes, but its the only option at this point.  A real upgrade would be sensible, of course.

You can use custom html/text widget in this case. Otherwise this is a custom code modification.
Make a suggestion on uservoice: http://oxwall.uservoice.com/forums/13756-ideas-for-oxwall
In the meantime this is considered as a custom code modification. You're free to do that on your own or hire a programmer. You can do that here: http://www.oxwall.org/market/specialists

Also you can make a post in the custom code modification section of the forum, probably some community member will assist you with that.