[exim] 20 messages to send, but only 10 minutes to do it in

The challenge: 20 messages to send, but only 10 minutes to do it in
(before another coin drops into the telco's coffers).

So let's use "parallel processing". Instead of only one smarthost,
I'll add my pal in Cal. to the list. That queue will be mincemeat in
no time, no?

Checking things here on Debian, it looks rather monolithic though.

I bet at the least I'd have to move half the queue to a different
directory and start a different exim process or something.
May still be able to do that with my Limited Edition Brain, but don't
want to push my luck.

PS: 20/10: assume modem but real bottleneck is slow SMTP transactions.