extracting Malaysian trumpets

I am going to be breaking down my 20g high tank to replace the 
substrate.  I have been having rather persistent problems with crypts in 
this tank and I feel I have little choice.  Thanks to some advice I 
received on this list, I stepped up my water changes and reduced the 
nitrate levels in the tank to about 10-20ppm (thanks, Karen), but the 
improvement was only short term, and the crypts are melting again.

So, I want to replace the gravel with a sand/laterite mix, and I want to 
take the Malaysian trumpet snails that are currently in the tank into the 
new tank with the other living contents.  How can I get them out of the 
gravel?  I have an idea which is to place the gravel in a bucket with 
enough Miracle-Gro to bring the nitrates up to about 60ppm, thus forcing 
the snails up where I can get at them.  This doesn't sound particularly 
elegant, and I was wondering if anyone had any better ideas.

Thanks in advance,