KBPsen:
I've seen it done on a DC-10 #2 - using a cherry-picker.

At least you are fairly safe inside the basket. I remember once doing a visual inspection of the fan and suddenly hearing the woosh of bleed air. I got out of there and back into the cherry picker rather swiftly.

In a program to save several million € a year we have increased our compressor wet wash frequency from once every three months to once every two weeks. Apparently the effect on fuel burn is quite big. Maintenance had to invest in additional rigs for that though, still saves a lot of money. Engine types mainly CFM 56 and PW4000, a few V2500 thrown into the mix as well.