perhaps invitations could be given to the teams that finish in the top six in spl who do not qualify for europe (along with welsh top two, 3 from LoI and 3 from IL). I think that would be the 5th and 6th place finishers in the spl.
if the setanta was expanded it might allow clubs to get more benefit from it like the rugby crowd do with the magners league. to cut down on costs perhaps start off with 2 groups of 5 who each play 2 home and 2 away games like the uefa cup for last few years. then semi and final.