Bleach takes elemental silver and moves it to ionic silver. The fixer then removes the ionic silver. It gets the ion from the Ferric Ammonium EDTA in the bleach ferric ion becoming ferrous (I might have the electron thing backwards). It also removes the dye formers that have not formed a dye in the colur developer, but I am not sure what the mechanism that does this is.

So I would guess that starter gets the bleach acting as though it has had a few rolls of film though it. It also usually is added to the replenisher along with water to make up the final volume of working solution. Replenshers are usually more concentrated than working solutions and replace the 'active ingredients' as they are incrementally added.

One way to 'fake' the starter action might be to fog some c-41 films and then develop in a b&w film developer to get lots of elemental silver, and then let them soak in the blaech. There should be lots of elemental silver to cut back to it ionic form , and oodles of uncoupled colour formers to digest. I don't quite now what the dilution amount of water should be used to take your replenisher and make a working solution. There are instructions for big photo labs to check thier solutions with hygrometers, but that is beyond the realm of most of us here.

Sorry, but I don't know how many exactly would be required. This thought comes to me from using Harveys 777 b&w developer, which has to be 'saesoned' with a couple of wasted films if you are mmixing it from a fresh bath. With 777 you keep the overflow from after the replenishment is made, and use the 'old gunk' to start the next batch after the first batch with film seasoning is done.

A wierd alternative that the Harveys route suggests is to beg some bleach overflow from a friendly minilab operator to act as your starterless working solution blaech. Start bleaching with this route with perhaps 1/2 to 3/4 of the tank made up of used 'munge', and then replenish from there.

C-41 bleaching can be visually inspected under tungsten everyday indoor lighting, after the film has been in the bleach for a minute of so. You can see whenthe film has bleached. If it has not bleached in the specified time, bleach longer, and next time add more replenisher.

I do/have done home brewed c-41. Presently my bleach is e-6 bleach, of which I I found three jugs to make 5l each at the HHW depot re-use shelf when I was dropping off used fixer one day. Once that is gone I will be back to my old bleach method with uses 80g of K ferricyanide and 20g of K Bromide per liter of bleach. I woul mix 2L at a time, and make 1L the working solution, and the second L the replenisher, adding 45mL per 80 square inches of film processed. I would harvest the overflow and when the 1L of replensiher was gone, turn the working and overflow into the HHW depot. This is C-22 belach, the precursor to C-41, and it works faster; 2.5 mnutes to the e-6 recommended 6 minutes as I recall.

I believe E-6 bleach is rated to 30 rolls of 80 sq in before it exhausts without replenishment, but I play it safe, and turn it in to the HHW after I have done 25 rolls.