How to use params with slashes with Sinatra?

Question

Playing with sinatra, I'm stuck on a little problem : when I use params with slashes, it confuses the router engine. So is there a nice way to handle this kind of param without having to encode it ?

The code looks like

get 'add/:url' do
   #....
end

And I intend to get something like /add/http://sctackoverflow.com/ working