If you really need to run a batch job you can do it as a restricted url handler; but if you need to run batch jobs, you're working against the grain of GAE.

Look at it this way, most batch jobs are prompted by a need to either import or export data; which is perfectly doable with GAE by having URLs for loading and reporting.

If you need to load gigabytes of data and run hours long procedures on it, GAE is the wrong tool.