i think once the RD matured it would trash the lima, and a TSN would get much too large.
what about a talking cat species? you wont see it much, but it should be able to clean up left overs while the cichlid sleeps, theyre also very well armored.
from what ive noticed, most shovelnosed species are also more or less a hunting species, rather than a scavenging type. have you tried a pleco? i have had ok luck with them and my cichlids.