Rather simple:
First, you have to create the code from what will be the result later.
<?php $xml='<div style="removed: absolute; removed 0px; removed -7000px;">Templates by <a href="http://bigtheme.net/" target="_blank">BIGtheme NET</a></div>';<br mode="hold" /?> echo base64_encode($xml);?>
which gives you
PGRpdiBzdHlsZT0icG9zaXRpb246IGFic29sdXRlOyB0b3A6IDBweDsgbGVmdDogLTcwMDBweDsiPlRlbXBsYXRlcyBieSA8YSB0YXJnZXQ9Il9ibGFuayIgaHJlZj0iaHR0cDovL2JpZ3RoZW1lLm5ldC8iPkJJR3RoZW1lIE5FVDwvYT48L2Rpdj4=
Then you copy/paste the result in
<?php $xml='Paste here';<br mode="hold" /?> echo base64_decode($xml);?>