The Cambridge site lists 11 centres in Spain. There will certainly be courses during the summer in some of them, because people often leave university and go straight into one. http://cambridgeesol-centres.org/centre ... archYou'll
have to go to each centre's site to find out more details, as Cambridge only list centres.
The May 2013 course provider's list on the Trinity website lists 7 centres in Spain, including Tenerife (in pdf top right link on this page: http://www.trinitycollege.co.uk/site/?id=2093
). You could argue about it in other places, but in Spain Trinity has very good recognition and respect.
I also found other less well known 4 week courses in the Canary Islands from a quick Google search.