I use "access_combined" for my GAE projects.
http://splunk-base.splunk.com/apps/54158/splunk-for-google-app-engine
I don't think there's a better solution than what you're doing - create your own extractions. Feel free to share them as an app here on splunkbase when you get them working!
ok I think no-one has never had this problem; I think I am developing my own type then I will share with you!