Font size

Hi!

In fckconfig.js I can modify the sizes of fonts att this line:

FCKConfig.FontSizes = '1/xx-small;2/x-small;3/small;4/medium;5/large;6/x-large;7/xx-large' ;

but how do I do if I would like to use pixles instead?
For example:

FCKConfig.FontSizes = '10px/xx-small;11px/x-small;12px/small;13px/medium;14px/large;15px/x-large;16px/xx-large' ;

I know that I cant do like that (ive tried) but can any one tell me how I can solve this problem?

Regards
Millvi