I lean both ways on this.
It's not a terrible idea. But your problem isn't clans not wanting to fight for you, if you attack someone that is at war with some one else it is much easier to get mercs, BUT you really need to do the ground work.
Strat is 90% politics. I know that when I attack some one or something I can rely on a lot of Hospitaller, Australis, Hate, ATS, FIDLGB, Kapikulu, Templar, TKoC, Occitan, KUTT and Chaos guys and gals coming out to bat for me because I've taken the time to do things for them and go talk to as many of them as possible.
When you have a battle and you don't have a name no one shows up, so you have to go on a Presidential campaign selling why people should come and help.
Best thing to do is make sure you have fun gear so everyone has a good if not silly time.