can't, need to adjust the mysql ini file (see here)
you may also want to look at your code to see if there are optimizations that you can make, like ensuring that you have the connections open only when you need them and close them (and free memory) as soon as your transaction(s) is/are complete. For that you need
[man]mysql_free_result[/man] and [man]mysql_close[/man]
Also look at optimizing where you query. If you constantly query to build a dropdown and it doesn't changem much, then perhaps you could get the data from a local array or textfile...