I'm surprised to hear you say that. I did research and I didn't come across any indications that they would be difficult to get eating prepared foods.
I knew that they weren't fussy about nori, but most of the websites I looked at spoke positively about they accepting spirulina and flakes.
He was definitely interested in the flakes when I fed them this afternoon, though I'm not sure if he actually ate any of them - he swam into a cave when the other fish started swimming around and eating aggressively.
Right now there is enough filamentous algae on my rocks that he doesn't need to eat prepared food. I scraped my tank before I took that photo but the back looks a little like astroturf. He's already picking at the glass and some of the rocks. If all else fails, I'll see if Dom will come over and work his voodoo fish eating magic.