Forcing blockland to use my static IP, not my public?
I believe by static IP you're referring to your private network IP. This is an IP address that is not useful to anyone outside of your local network, aka no internet players could connect.
When you port forward, you're telling your router "anything sent to our shared public address at this port should be forwarded to this one static address inside our local network", which you set your computer to identify as when you disable DHCP and set a static IP address.
Blockland will respond to anything sent to the port (default 28000) it is listening on, regardless of what IP address the sender refers to it as (local IP address for LAN, public for internet).
My router is stupid and won't let me use my static IP.
This seems to be a different issue than your title. If you set a static IP address and are able to use the internet, you've done it correctly and your router is able to communicate with you and visa versa. If you set it and you are unable to use the internet, you've configured something incorrectly. In this case, the router is likely using a different subnet than whatever guide you followed (192.168.
1.xxx instead of 192.168.
0.xxx for example). Alternatively, the static IP address you picked may already be in use (randomly assigned via DHCP).
If you want specific help, you're going to need to describe your problem more. What exact issues are you having?