I've recently stumbled upon String::Format. Although I haven't used it yet, I believe it to be a possible solution for such cases. In a nutshell:

#!/usr/bin/perl -w
use strict;
use String::Format qw(stringf);

print stringf( "%a->%o->%a\n", a => "apples", o => "oranges" );
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I don't know how fast it is, though.

UPDATE: I like the %(foo) solution even more!