Hi There, if i understood correctly, here is what you are looking for...

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To use a file in a filesystem for swap space, choose the swap space
size that you want for this swap area (up to 2 GiB on x86) and then
enter (as described in 'man mkswap'):
dd bs=1024 count=1M if=/dev/zero of=/path/to/swapfile.n
This writes a 1 GiB file (1 MiB * 1024) to "/path/to/swapfile.n".
You can do this multiple times to use more swap files on large-memory
systems. Swap files cannot be sparse; they must be fully allocated
before using them.
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** more on http://www.xenotime.net/linux/doc/swap-mini-howto.txt

-ilan