from what ive read they will do fine without a host, and also its good there are no larger fish, unless they are huge fish that can support it, it will likely be harassed to death if the remora thinks it will be a host which happens around if there the same size.
my 2 cents
JL site says
"Echeneis naucrates
Brought in as a special order originally. This guy has a voracious appetite, he will need a very large system, ideally with tank mates capable of competing for food. Approx. 9""
and read all this
http://www.wetwebmedia.com/remorafaqs.htm