max_execution_time & header

I'm trying to backup a huge amount of data comming from a MySQL database. It seems that my script times out before it is done. I'm unable to persuade my ISP to raise the max_execution_time and thought of using redirects instead (header). I've written a script that backs up 500 rows and then redirects to a simple script that in turn redirects back to my main script (with an offset). I still run into the max_execution_time!!! I thought it would be reset as I redirect to another page. Any help appreciated. Regards, Peter Schumacher