Selectively choosing the default gateway

The setup:

Interface 1 = Public. ADSL, gets an IP of 203.1.1.1 from PPPoE. Also has a block of additioanl IP assigned, 203.2.2.0/24.
Interface 2 = Inside. 192.168.1.0/24
Interface 3 = AlternateOut. Statically assigned the IP 10.1.1.1. There is a gateway on this network, 10.1.1.254, but currently no routes have been configured on the MikroTik.

There are a few statically NATed systems on the inside network; dst-nat and src-nat rules have been set up for these (so 192.168.1.61 maps to 203.1.1.61, etc)

All other traffic goes to a masqurade rules, so goes out interface Public as 203.1.1.1

What I want to do is keep the statically NATed systems the way they are (that is, their traffic goes out over interface Public through the appropriate NAT rules) while any other system that sends a packet out to the internet gets it routed through AlternateOut.

How can this be done? If I set up an alternate static route to 0.0.0.0/0 through 10.1.1.254 it will either always get used or never get used, depending on how it compares to the route to 0.0.0.0/0 via Public. Is there some way to selectively route in this manner?

Yes It is possible, you have to use mangle and set another default route in another routing table, here is an example:
http://wiki.mikrotik.com/wiki/Load_Balancing_over_Multiple_Gateways

Thanks, that looks like what I need.