How to open a page in a new tab with Post params

I have been reading the documentation and I can not find how to open a page (most likely .php) in a new tab with POST parameters from my WebCore application without recurring to appending DOM elements to my main WebCore app.

I usually do this in php or asp applications, so the user can check the new page (most likely a report), print it or whatever and then close it, all without affecting the main application window in the browser.
My customers like to have multiple tabs open at the same time with different reports by my applications and now I want to implement it using WebCore.

I avoid using something like an url label, because that would make all parameters visible as part of a get request in the address bar of the new tab. Using a form element with method="post" and target="_blank" in the caller html does the job, but I want to implement it completely in WebCore if possible.