I knew there would be a nice XML way to do this. Merci Beaucoup, Muchos Gracias, Vielen Dank, Spacebo, Arigatou, Kiitos, Tusen Takk, Obrigado and Sanctuary match!

In fact for temporary hacking use at least it is possible to omit log.xml - the following code works:

$logfn = '/path/to/log.data';
print Dumper (XMLin(<<EOENT ));
<?xml version="1.0"?>
<!DOCTYPE log [
<!ENTITY data SYSTEM "$logfn">
]>
<log>&data;</log>
EOENT
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Dingus