[Exim] pipe deliveries and multiple recipients

I have the following sporadic but annoying problem:
An address is (via /etc/aliases) expanded to a list of local users. Each
local deliviery is done sequentialy via a pipe transport. If one of the
pipe transports hangs for some obscure reason, it blocks the delivery to
the other recipients until it is killed after the pipe tranports timeout.

Is it possible make this non blocking, so that a hanging pipe delivery
won't stop everybody from getting mail? Kind of parallel delivery?

Michael