Hab's rausgefunden:
[autoit]
$sData = "--" & $sBoundary & @CRLF
$sData &= 'Content-Disposition: form-data; name="einFeld"' & @CRLF & @CRLF & "FeldWert" & @CRLF & @CRLF
$sData &= "--" & $sBoundary & @CRLF
$sData &= 'Content-Disposition: form-data; name="nocheinFeld"' & @CRLF & @CRLF & "Weiterer Wert" & @CRLF & @CRLF
$sData &= "--" & $sBoundary & @CRLF
$sData &= 'Content-Disposition: form-data; name="drittesFeld"' & @CRLF & @CRLF & "Irgendwas" & @CRLF & @CRLF