How would one go about routing a recently-purchased /24 block of IPv4's to a single server? The server is colocated in Zare.com, and the BGP session is already set up and announced.
"the BGP session is already up"
Between which peers? We might need some more information here.
On the other hand, it will all depend on how the network admins built their network. You'll have to ask them, I'm afraid. I can think of these cases, and I'm certain that there's plenty more ways to do this:
Same Subnet: --> ARP Alias
If that server and its default gateway are in that very same /24, you probably won't have to actually route. In that case, you may add additional IP addresses (sometimes called "secondary IPs", "ARP alias" or "IP alias") to the NIC that server already has in that /24 subnet. The upstream router will ARP for these addresses, and the server hear and ARP-reply to them.
Multinet: --> ARP Alias
If the server is on a different IP subnet than the /24 AND if the network admins have implemented "ip address secondary" for that broadcast domain/VLAN (i.e. running multiple IP subnets on the same broadcast domain, sometimes called a "multinet"), you may do as above: add ARP aliases on the given NIC of the server.
different Subnet: --> Routing
If the server (resp. the given NIC) is on a different subnet than that /24 AND if there is no multinetting, some routing will have to be involved, and you'll have to talk to the network administrators.
ask the network admins to add a static route for the /24, with your server's IP as the next hop, and - if needed - to take appropriate action on their further upstream routers, such as redistributing/injecting that static route into whatever (internal) routing protocol they may be using.
implement a dynamic routing protocol on your server (probably External BGP), and have it "talk" to the upstream router(s), announcing the /24 as being reachable via your server. That requires even closer cooperation with the network admins.
In either variety of routing, the IPs themselves will also have to be implemented on the server. That might be as additional addresses on the NIC or some subinterface thereof, on some kind of internal loopback device; that all depends on your servers' capabilities, and would be beyond the scope of this board.