SP10 Modal Dialog - set Document Mode

I have customized a button on the SP10 document library via Elements.xml and use:

       CommandAction="javascript: (function () {
            var o = {
              url:'/_layouts/UploadSplitFile/UploadSplit.aspx',
              title: 'Upload Split',
              width: 600,
              height: 600
              };
            SP.UI.ModalDialog.showModalDialog(o); }) ();"/>

to open a modal dialog box with my page.

Everything works great, BUT my page needs IE11 document mode. Which is fine, when I open it without the modal dialog (I use my own master page with <meta http-equiv="X-UA-Compatible" content="IE=edge"/> in the header).

But when I then open the same page in the dialog box, it takes the document mode setting from the document library page, which is set to IE=8.

Is there any way I can tell the modal dialog to open my page with IE=edge programmatically? (Changing the .master is not an option)

Thanks in advance, Simon