I've configured my site to serve compressed content by putting this line in .htaccess

AddOutputFilterByType DEFLATE text/html text/plain text/xml text/javascript text/css application/javascript application/json

This works perfectly for almost all files except a few large JSON files that are above 200Kb. For some reason they are not being compressed. I see that they don't using the net tab in firebug and the Network section in chrome.

So as a workaround I thought I could compress these files offline and have Apache read them compressed.
What tool should I use to compress them? is the linux gzip the one? any special flags or something I should use?
What should I put in .htaccess so that the server would know to serve these files with content-encoding gzip ?