What I wanted was possible.

sub build_args() {  # Based on fastolfe's answer
    my $data = shift;
    my $ptr = \%The_Big_Hash;
    my $me  = pop @_;
    foreach my $host (@_) {
        $ptr = $ptr->{$host}{deps};
    }
    $ptr->{$me}{args} = [ @{ $data } ];
    $ptr->{$me}{deps} = {};
}