Modify additionalHeaders for mlb_newsevent

I would like to change dinamically the headers of a page that downloads an ICS file using the extension mbl_newsevent. As you may know, usually the ICS filename is Event.ics and I want to change that to Event_1234.ics (where 1234 is the the tt_news uid). My code for that:

singleicsevent {
    config {
        disableAllHeaderCode = 1
        additionalHeaders = TEXT
        additionalHeaders.value = Content-type:text/ics | Content-Disposition:    attachment; filename="Event_{GPvar:tx_ttnews|tt_news}.ics"
        additionalHeaders.insertData = 1
        no_cache = 1
        xhtml_cleaning = 0  
    } 
}

But that does not work as additionalHeaders is of type string and that is ignored. Any suggestions how I can do that only with typoscript?