I'd be wary of working with someone who thinks that the idea--an idea he cannot execute on without your/someone's help--is worth 99%. That's a faulty assumption, and it would prompt me to ask how many other faulty assumptions he's operating under.
Give him a few data points--links to articles that discuss dividing equity stake in various early-stage scenarios. Include some famous company founding stories. It's possible that he'll come around and realize that the idea is merely the kernel of what might become a great business someday.
If he's a quick study, he'll realize that he needs other people to make his vision a reality, and that he'll need those people for the long haul. If he offers merger equity, it will be easy for his critical team members to walk away, and that's something he should want to prevent at all costs.
If he still insists that his idea is the key driver of the business, he misunderstands business. Walk away.
(Oh, and here're my two cents on the split: pre-product, pre-revenue, pre-customer, pre-partnership, with an unproven entrepreneur, you should be looking for between 45% and 50%. And you should be vetting him to ensure that he can complement your skill set in critical areas.)