Okay now mind you i'm by no means an expert. Could'nt you add the fish to the 55g. while they are in there for say 4 to 6 days you could add amonia to the 5g building up a large bacteria population just a couple of drops every day to get small smikes. then you could take the all the gravel from the 5g after 4 or 6 days and put it in the 55g that way you've built up a little amonia in the 55 and all the bacteria are not going to die from not having enough food. I mean why start from the begining if you don't have to. Just remember to do one vary large water change on the 5g before you dump it in the 55g to the get the Nitrates out. Then ether dump it in the 55 or even tie it in those little mesh bags or something.
Well I could be totaly wrong but worth a try.