if your swap partition is big enough you can add the following to you
/etc/fstab file:

/dev/<swap device>	/tmp	mfs	rw,-s<memory size>	0 0

Just make sure that you will still have enough space for your swap
area and that mfs has been compiled into your kernel.

e.g:

/dev/sd0b	/tmp	mfs	rw,-s102400 	0 0

gives you a /tmp directory of 50Mb size on swap partition sd0b

cheerio Berndt