We use suPHP in all of our servers. So you can modify your php.ini value very easily!
All you need to do is just set the suPHP configpath so that all other subdirectories in your public_html takes that php.ini as its default configuration file. To do this put the following line in your .htaccess:
<IfModule mod_suphp.c>
suPHP_ConfigPath /home/username/public_html/
</IfModule>
Replace "username" with your cPanel Username.
Then create php.ini file under public_html folder.
You can provide value in php.ini to override any php limit. For ex.
post_max_size = 1000M
upload_max_filesize = 1000M