Just implement a plugin that clashes with $c->stash, and override it with a method that filters things in the stash using a regular expression. This way you'll get more control over what the stash dumps into your view modules, with something easy as $c->stash( qr/.../ ). Of course, with no arguments, $c->stash() will dump everything out, as expected.

All code is untested, and extremely experimental.

package Catalyst::Plugin::Stash::Filter;

use warnings;
use strict;
use NEXT;

1;
package Catalyst::Engine;

use warnings;
use strict;
use NEXT;

=item $c->stash

If the first argument is a hashref, returns a hashref containing only
data keys that matches $_[0]->{FILTER}. Otherwise, returns a hashref
containing all your data.

    $c->stash->{foo} ||= 'yada';
    print $c->stash->{foo};

=cut

sub stash {
  my $self = shift;

  # this makes the real stash() method magic...
  my $stash = $self->NEXT::stash();

  # this filters out everything unwanted or unknow...
  if( UNIVERSAL::isa( $_[0], 'HASH') && exists $_[0]->{FILTER} ){
    # $strip is just a boolean.
    my( $criteria, $strip ) = ( $_[0]->{FILTER}, $_[0]->{STRIP} );

    ## err... "borrowed" from Andy Wardley's AppConfig::State module.
    ## Original comments follow.
    ## thanks, Andy.
    # extract relevant keys and slice out corresponding values
    my @keys = grep(/$criteria/, keys %{ $stash });
    my @vals = @{ $stash }{ @keys };
    my %set;

    # clean off the $criteria part if $strip is set
    @keys = map { s/$criteria//; $_ } @keys if $strip;

    # slice values into the target hash 
    @set{ @keys } = @vals;
    $stash = \%set;
  }
  return $stash;
}
1;
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