Wadder was replaced by customize mii, which IIRC basically does the same thing but it's a bit easier to set up and use.
While customize Mii can build forwarders, "advanced" or complex forwarders require dev kit installed, and even those forwarders aren't as optimal as the ones you can compile directly. The issue is that it's a real pain in the ass setting up devkit, the latest libraries are broken and finding the latest versions without bugs is a real challenge. Luckily, ModMii can build advanced forwarders for you. Go to modmii classic's advanced
downloads to build a forwarder dol or forwarder iso. You can feed modmii with whatever paths you want for your forwarder, and modmii will save a copy of a base/template wad and hex edit it with the paths you identify. Then you can take the dol and inject it into a wad using customize Mii or similar tools.