Question : Setting up Alternate Exchange Email Flow "Route"

We had a situation where our primary ISP had a 6 hour internet outage.  This meant our employees email was not flowing outbound and inbound.  We do have a seperate broadband carrier for certain things.  

What we would like to do is if this ever happened again direct our mail server through that carrier as a temporary solution.  

We have a few concerns and I thought I'd post here to see if anyone else has successfully done something like this.

Concerns:
1)  It is using a different carrier so the IP addresses will change, we'll need a second IP for the public facing server (A) record (MX) record.  Can we do that with low priority or something?
2) Same question as above for incoming email.  Will DNS become a problem?

VERY interested to hear any real world implementations of this type of backup solution in case of the primary ISP completely falling off the map like ours did.

Thanks!

Answer : Setting up Alternate Exchange Email Flow "Route"

1. You use 2 SMTP connectors:
http://www.amset.info/exchange/smtp-connector.asp
http://www.microsoft.com/downloads/details.aspx?FamilyID=C092B7A7-9034-4401-949C-B29D47131622&displaylang=en

2. Incoming mail can be handled by 2 different MX pointers, primary with a low value (high priority) and the second for the alternate route.