Checked back through the thread and didn't see mention that this was tried, so: a good way to transition from live to f/t is once a snake is feeding well on live (mice or rats; it seems your snake has no strong preference, which is good) is to offer freshly killed prey. It smells live, and looks somewhat live, but has none of the risks of live. It is also a step on the way to getting a resistant snake to switch from hunting to what is sometimes basically scavenging (eating a long-dead prey item from the ground). Feeding a bunch of random stuff (size and species) is indeed getting food into the snake, but isn't exactly a plan for weaning him onto a sustainable long term diet.
Feeding fresh prekilled isn't exactly something all novice keepers want to get into (both because of the psychological hurdles, and also the cost of equipment needed to humanely euthanize larger rodents), but taking on the care of a live feeder isn't a recommended novice situation either. It is really unfortunate that breeders will sell live-only feeders to new keepers.
One other option to try is to get frozen feeders from a different source. It has been my experience with a range of colubrids and boids (the only pythons I've bred are blood pythons, once, which I had a friend sell for me and so I lost track of their ongoing feeding habits) that some snakes will refuse some f/t feeders from one source but readily take them from some other source. Likely, the scent of the rodent matters, and rodents from different breeders will have different scents.
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