Australia has a problem: there are too many Kangaroos. The population of Kangaroos needs to be limited, just like the population of deer needs to be reduced in America. While there may be alternatives to culling, artificial feeding is not one. Artificial feeding would actually help increase the population, which is not what Australia needs right now.
No, it would not be an inadequate alternative to artificially feed kangaroos instead of executing a cull. This would allow for a feeding period and the kangaroos would not be able to breed and overpopulate to the degree that a cull was required and necessary to keep their numbers in check.