it should be fairly easy. you’ll need to implement your own Logger and LoggerFactory. you will not have to change existing code at all.
after doing that you’ll need to implement StaticLoggerBinder to return your logger factory and class name. if you download the slf4j zip file then you get the source for all the implementations too, just have a look at the StaticLoggerBinder in slf4j-log4j for an example.
have a look at this link for details : http://www.slf4j.org/faq.html#slf4j_compatible