how to change/fake the time for next commit ?

Hi Git list,

I'd like to recreate a git repo with kernel version, using exclusively tar.bz2 files.

I already did such approach in the past by script, but usually the dates of commit are the timestamps of current tar imports. I'd like the date of commit to match any date I would give (without changing the time on my linux system): the date I would give would be (of course) the date of the released version.

example: date of 2.6.23.8 release was 2007-11-16 18:16 UTC, so if I import linux-2.6.23.8.tar.bz2 into a dedicated "2.6.23.8" branch, I'd like the commit to have "2007-11-16 18:16 UTC" as date.

Is there a way to do this, by plumbing or porcelain ?