update

I am dumb, the one below does not work 'cos I put a my in the BEGIN block, when good habits turn bad! Without the my it works a charm

>perl -le'BEGIN{$BASE="are belong to us"}
          use constant BASE => $BASE; 
          print "all your base ", BASE'
all your base are belong to us
>
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original message

I though that would work too but it does not for me

> perl -le'BEGIN{$BASE="are belong to us"}
         use constant BASE => $BASE;
         print "all your base ", BASE'
all your base
>
# but this does
>perl -le'use constant BASE=>"are belong to us"; 
          print "all your base ", BASE'
all your base are belong to us
>
[download]

But I guess the OP was after something more flexible

Cheers,
R.