plat
Ready to race!
What about those cheap mesh lumbar supports they sell on ebay and amazon?
They are about $5 to $10 and would at least let air circulate.
eg: http://cgi.ebay.ca/2-X-MESH-BACK-LU...396587500?pt=LH_DefaultDomain_0#ht_7102wt_952
My mother has one in her Civic. For a tall person like me, it makes me sit in a more upright position so I loose headroom. Personally, I don't feel comfortable using it.