[Exim] Directors + suffix option

Hi,

I'm trying to make a director for passing certain prefixes to a transport,
mainly those of a mailing list usage, e.g.

-subscribe-request

But I don't think the suffix operator likes the two -'s... is there a way to
"escape" the second -, or can you simply not have two -'s in a suffix?

Cheers,
Andy.