Actually I found a way where the EXTRAs work.
This is a combination of an answer I found here regarding ACTION_SENDTO
http://www.coderanch.com/t/520651/Android/Mobile/no-application-perform-action-when
and something for HTML which I found here:
How to send HTML email
(but the variant of how to use ACTION_SENDTO in this HTML post didn't work for me - I got the "action not supported" which you are seeing)
    // works with blank mailId - user will have to fill in To: field
    String mailId="";
    // or can work with pre-filled-in To: field
// String mailId="yourmail@gmail.com";
Intent emailIntent = new Intent(Intent.ACTION_SENDTO, 
                                    Uri.fromParts("mailto",mailId, null)); 
emailIntent.putExtra(android.content.Intent.EXTRA_SUBJECT, "Subject text here"); 
    // you can use simple text like this
// emailIntent.putExtra(android.content.Intent.EXTRA_TEXT,"Body text here"); 
    // or get fancy with HTML like this
emailIntent.putExtra(
             Intent.EXTRA_TEXT,
             Html.fromHtml(new StringBuilder()
                 .append("<p><b>Some Content</b></p>")
                 .append("<a>http://www.google.com</a>")
                 .append("<small><p>More content</p></small>")
                 .toString())
             );
startActivity(Intent.createChooser(emailIntent, "Send email..."));