Yeah that's the theory. Don't know how rice might work, maybe it would sink. Oatmeal? Panko bread crumbs?
Just realized you're in Japan. Availability of stuff over there might be totally different and stuff like bunker oil hard to find.
Mixing up a brew like that IS a real mess, and if you're in an apartment complex.....
I would try to find frozen stuff, maybe a block of frozen shrimp/clams/ mussels? Or try and get some discards from a fish market?
The advantage of frozen is that it will melt over time, gradually feeding chum into a slick. I suppose you cold get fresh fish guts and put them in an onion bag in a 5 gallon bucket inside the boat, and dip it over the side every once in awhile, but that's going to be a mess and a lot of work too.
Since you're in Japan you could send Ian Mackay in Ashiya an email. His site is here
Japanese Fishing Tips & Tackle News
He discusses gear used for chumming over there, and sounds like a good guy to know. There's a link for his email there on the main page.
Good luck! Can't wait to hear stories from your adventures.