You're on the right track. First, bless the object. Then, use the nifty can method:

sub new {
    my $class = shift;
    my $self  = {};
    bless($self, $class);
    my %params = @_;
    foreach my $token (keys %params) {
        if (defined(my $sub = $self->can($token))) {
            $self->$sub($params{$token});
        } else {
            warn "We don't have any \"$token\" thingies 'round these p
+arts!\n";
        }
    }
    return $self;
}
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When I'm feeling this paranoid, I usually keep around a list of valid fields, but this is a good approach. The only drawback I see is that someone can call an arbitrary (non-accessor) method by passing the right parameters to the constructor.

There are ways to get around that, too.