Preserving phenotypes without a mother

I haven't done a mother plant or clones for a good few years. But I understand your question and have done what you want to do. I found the original clone was a good producer. The other clones that I let veg probably produced 2/3 of the mother if not less. The best way I found was I kept a mother plant in one tent under a weak ish light think it was a cfl bulb. I took clones from that one and rooted them. They produced a decent crop. I managed to keep the mother for about 18 month and ran clones from her during that time. Then I allowed the mother to flower. I think with the way you want to do it is that the plants seem to get weaker the more you clone from clones.