A new way to make periclinal chimeras in citrus is given here.
日 植 病 報 60: 82-88 (1994)
Ann. Phytopath. Soc. Japan 60: 82-88 (1994)
OK, 1994 isn;t new but it is new to mr, The procass was developed to give disease resistanc in citrus by giving a good variety a coating of a disease resistant variety, But it seems to me it might work on making good citrus varioties a coating of a cold tolerant variety like ponciris, The publication says 1/6 of plants made this way were periclinal chimeras,
One would need to use a good varity of citrus that has nucelar seeds, No problem finding those,
I don't expect the rresulting plants to be hardy in one 6 where I live, But maybe zone 7 or 8? Maybe anywhere PPrague is hardy?