I think what you want to do isn't directly supported by Exporter.  But you could of course reinvent the parts of it you need in slightly modified (and simplified) form:

package Foo;
use strict;
use warnings;

sub import {
    # print "Foo::import(): @_\n";  # debug

    shift @_;  # first arg not needed here
    my $dest = caller;

    for my $what (@_) {
        if ($what eq ':transforms') {
            no strict 'refs';

            for (qw(transform_one transform_two)) {
                
                *{"${dest}::$_"} = *{"Foo::Transforms::$_"};
            }
        }
        # elsif ...
    }
}

package Foo::Transforms;

sub transform_one{ return "transform_one(): @_" }
sub transform_two{ return "transform_two(): @_" }

# ...
1;
[download]

#!/usr/local/bin/perl -l

use Foo qw(:transforms);

print transform_one("xyzabc");

__END__
$ ./831686.pl
transform_one(): xyzabc
[download]

The difference to the other suggestions is that you wouldn't need to go exporting indirectly via the Foo namespace.  In other words, you could have routines of the same name in Foo::Bar, Foo::Transforms, etc. without risking name clashes in the intermediate Foo namespace... (of course, the mapped final names in the destination package would still have to be unique).