Wordpress need to create a php.ini file on CCGI space and point .htaccess to it

[#1]

Hi,
  I've been having some errors with my Wordpress site caused by tmp running out of space. I raised a call with Plusnet and they came back with:
The actual tmp file is a global temp folder on our server so your changes would not impact the errors you are seeing , a cron task is scheduled to delete all this data periodically so you will find that the errors may disappear, we have no plans to increase the /tmp folder which is currently 6gb  so to avoid this issue, please look into having your own phpini file and assigning the /tmp directory to your own webspace and on request we  can add a cron task to clear out this directory periodically for you.
I've done some googling and found out I need to create my own php.ini file with the following code in it:
upload_max_filesize = 50M
post_max_size = 50M
But I don't understand where I need to put this file in my CCGI space. i.e. does it go in the root of my ccgi folder, or in the wordpress (wp) folder?
I also have to edit the .htaccess file to point to this php.ini with code along the lines of:
suPHP_ConfigPath /home/your_user_name/public_html/php.ini
Again I'm not sure how the example path relates to my CCGI space.
Can anyone give me some pointers? I've been looking at the following link:
http://wordpress.org/support/topic/phpini-problem

[#2]

I suggest using the script posted here in the "/tmp file filling up and causing scripts to fail" thread on this forum. The script needs to go into the top-level directory of your ccgi webspace ( / ).
There is no need to "point .htaccess to it", PHP scripts will use it if is found in the appropriate directory