High Limit Credit Cards to help with down pmt

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Has anyone had experience using an AMEX Blue or other AMEX high limit card to help with leveraging a purchase?

Some friends of mine are at the James Smith seminar this week and basically said that all they have really learned so far is getting high limit credit cards around 100K limit. She is a mortgage loan officer and on average she said conventional financing will only get you 80% down (as an investor on average) and the high limit credit cards can possibly get you 15% and you can put 5% down in cash. The idea is that the LTV you get on refinance is higher (more like 95% compared to 80%) so you refinance after you purchase.

Anyone use this method? Does it work? Any thoughts on pitfalls, etc?