Post data to webform

Hey!

I am having a trouble getting POST data to a Webform. Right now I am sending all the data through GET method which is only the temporary solution. My Webform is opened with colorbox-node modal window with a link like this: "Make contact". So this is obviously sending the data through GET method.
So do you know how can I open the Webform in modal window with sent POST data?

Thank you very much in advance!