So it can be done! Bod's site shows I can get there on BA and Adria via Paris on the outbound and return via Zurich into LCY, with 6 hours in LJU.
But that's a lot of travel time - maybe a night in LJU on the Friday is not such a bad thing, so the TA is pricing up going direct on JP (Adria).
Thanx chaps.
James