but neither changes to the object nor the %ENVironment seem to persist.

Hm. The second part of that is incorrect:

#! perl -slw
use strict;

$SIG{ INT } = sub {
    print 'SIGINT called';
    $ENV{ fred } = 12345;
    return;
};

$ENV{ fred } = 0;

while( sleep 1 ) {
    print $ENV{ fred };
}

__END__
C:\test>junk10
0
0
0
0
0
0
SIGINT called
12345
12345
12345
12345
12345
12345
12345
Terminating on signal SIGBREAK(21)
[download]

Which probably means that I've misunderstood your intent. Perhaps you could post some code to demonstrate the problem?