...
package main;

use Interpolation;
my $foo = new Foo;
my $Foo = {};
tie %$Foo, 'Interpolation::general', sub {
	my $cmd = shift();
	no strict 'refs';
	$foo->$cmd(@_);
}, '$@->$';

print "x $Foo->{bar}\n";
print "x $Foo->{bar}{1}\n";
print "x $Foo->{bar}{1,2}\n";