The docs for MIME::Lite::HTML
don't make this clear at all, and I had to look at the source to suss what was going on...
M::L::H *doesn't* inherit from MIME::Lite - it just uses it....but the good news is that it returns a MIME::Lite object when you call the parse method, so what you actually want is this...
my $mailHTML = new MIME::Lite::HTML
From => 'Someone@anyplace.com',
my $MIMEmail = $mailHTML->parse('http://google.com');
$MIMEmail->attach( Type =>'text/html; etc. etc);