As far as I know, there is no way to fire off more than 2 spells in order, provided they are all active. It's simply a limitation/restriction of the macro engine.

There's a ton of info on this site and wiki discussing how people set their keys up. I personally load 2 spells per macro. Others will have 3 macros, all loaded with similar spells. From all my reading, I've never seen anyone provide a work around for this issue.