Cisco WAN :: 2960G Router On Stick And Routed Public Range?

I understand router on a stick for inter-vlan routing but where I'm having trouble is having one of the vlans be public addresses.  One of my clients has a rack in a colo where there is no router, i.e. their /24 public network has .1 of the network assigned to a colo router, then they have a 2960G switch in the rack that all the gear is connected to.  Public IP's are assigned to certain devices / servers with .1 as their GW.  Problem is, they also have a private range on the same switch with no vlans and things are a little 'cluttered' and there is no control of traffic.
 
The assets I have are a 2821 router with (2) GigE interfaces and the 2960G switch.  A /30 network is going to assigned on the colo gear to use to push the entire /24 down to the cabinet.  I'm going to NAT the local 10.100.x addresses on vlan 10 and I want the public traffic on vlan 20.  During a recent test, the private traffic worked as expected but the public traffic didn't work.  I don't need a complete config, more of a 10,000 ft. view of how this needs to be done so (a) traffic is vlan'd to keep things segmented, (b) I can static inside / outside public addresses from the /24 to reduce the number of public addresses being assigned directly to servers (some of this is unavoidable, but the less the better), and (c) I can NAT the local subnet to either to the /24 or the /30 (not much very much traffic in this way).
 
EDIT:  The switch is a C2960S, not G.  I cannot enable lanbase-routing, it is apparently unavailable.

*    1 26    WS-C2960S-24TS-S   12.2(55)SE3           C2960S-UNIVERSALK9-M