to be totally honest with you that sounds like about as soft as it's going to get, a little bit of oil might help (I've used baby oil before) but you're not really going to get it much softer without going to some type of pressure tanning which will cost the bucks... so to be honest you're most likely stuck. I have had some luck with pressure tanning but it takes a lot of time and cost a bit unless you do it in larger batches. My favorite is to just use the 2x4 and cinder block and keep at it until it gets close as the skin will soften a good deal when it gets good and wet.

Steve