Have you tried the snd-dummy module?
$ modinfo snd-dummy filename: /lib/modules/2.6.28-11-generic/kernel/sound/drivers/snd-dummy.ko license: GPL description: Dummy soundcard (/dev/null) author: Jaroslav Kysela <perex@perex.cz> srcversion: AFF1C8B79BA4E7C29AE9874 depends: snd-pcm,snd vermagic: 2.6.28-11-generic SMP mod_unload modversions 586 parm: index:Index value for dummy soundcard. (array of int) parm: id:ID string for dummy soundcard. (array of charp) parm: enable:Enable this dummy soundcard. (array of bool) parm: pcm_devs:PCM devices # (0-4) for dummy driver. (array of int) parm: pcm_substreams:PCM substreams # (1-16) for dummy driver. (array of int)