First, let me say you're a sick, sick being for thinking of this. Good work! :)

Change the line that reads

$code =~ s/\+/P++; /g;
[download]

To read:

$code =~ s/(\++)/"P+=".length($1).";" /eg;
[download]

You can probably do the same for \-, I'd think:

$code =~ s/(\-+)/"P-=".length($1).";" /eg;
[download]

By the way, wouldn't + become P++, and not $Inline::Brainfuck::p++? Maybe I'm reading your filter wrong...

I'm guessing the same technique would apply to the < and > filters, too.
--
Mike

Edit: By the way, I frontpaged this thread, THEN he posted a question I could answer. Normally, I wouldn't front page a thread I'm going to participate in.
Edit 2: Made node title more firewall friendly