The strategy below is hardly optimal, but it's funny as heck in a masochistic way.
1. Colonize 100-150 planets with super-breeder and Torian technology. Build some farms and get the planets to about 18 bil pop. Don't bother with defenses. Quantity has a quality of its own.
2. Max out econ with governments/custom points/federalism.
3. Build industrial plans.
4. Use industrial plants to build constructors non-stop.
5. Spam protected influence starbases and watch the AI suicide fighters into them.
6. Make peace.
7. Build more influence starbases and convert them.
The key idea is this:
If you can manage to get that economy up, you can build 30 constructors or more a turn. Since each AI who is at war with you can only kill about 5-7 constructors a turn at maximum, some of the constructors will get through and you eventually win through sheer numbers of protected influential starbases in enemy territory.