I've never found it to be that awkward to extend existing classes from java. Part of the problem in clojure are there are so many different ways to do it, all with different shortcomings.

For simple adding of a protocol to a class you can always just use (extend-class)

Proxies are simple and work well in other cases.

the gen-class documentation is a bit confusing, it helped me to look @ some examples. I used a different site that I can't find now, but this one seems helpful.

http://kotka.de/blog/2010/02/gen-class_how_it_works_and_how_...