I tried this as well last night, the only Beer I could find to work with the yeast in the ferminter was a Hop Brown Ale so I put the Texas Red into a carboy and poured the fresh batch right on top gave it a swirl and kept it around 70 degrees and this morning the air lock was going non stop.
Before I did this however i emailed my LHS and this is what he said:
It is possible to do this and in fact hundreds of years ago this is what brewers did before we discovered that yeast was what caused fermentation to take place. Now a days you can use this method if you plan on brewing the same recipe back to back in order to save on buying yeast. We recommend on reusing yeast from the primary fermenter and only to reuse the yeast cake 1-2 times as the yeast will get tired after awhile and because dead yeast cells start to break down after 4-6 weeks and can lead to off flavors. You'll also want the second batch you brew to be of similar style as certain yeast strains are only good for a few styles of beer and it might lead to and interesting results if you tried to go from a wit to a stout using the same yeast.
White Labs WLP001 and Wyeast 1056 American Ale are two yeast strains that have a very wide range of uses and would be good for reusing the yeast on. Have a good day,
I have also read that you want to a darker beer each time but then some people say it really dosent matter!