Even if you do this the SQL server might as well give you the low priority query back first if it executes faster.
What you can do when using mysql is SELECT/INSERT [LOW_PRIORITY | HIGH_PRIORITY].
See
http://dev.mysql.com/doc/refman/5.0/...rt-select.html for more information.
Why don't you just make a function in you script that executes your queries based on the priority you give them?