urn:mace:dir:attribute-def:eduPersonTargetedID only username part not scope

[damian.hall at canterbury.ac.uk]

I am currently using Shibboleth 2.5.0 and am having an issue trying to
transform the urn:mace:dir:attribute-def:eduPersonTargetedID to just
output the username part.

Currently the value getting passed back to the Shibboleth SP is
username\@domain, I cant seem to figure out how to filter the attribute
using the NameIDFromScopedAttributeDecoder. The final output should just
be the username, this then gets set in the REMOTE_USER field within my
server variables.

Any suggestions / help would be very grateful,

Many thanks
Damian