I've seen people suds their coils up with Simple Green and rinse it down, it takes lots of rinsing through the coil to get the suds out completely. Usually people take the cover and fan off of conventional condensers. I'm not sure if it takes anything special as far a being sure everything can get rinsed out with a mini-split though.
http://www.simplegreen.com/cleaningtips/pdf/148.pdf