I wonder if itemizing payments per service would help? You'd then only incur suspension for services you couldn't afford. Maybe this in combination with some form of prepays?

So maybe a couple of EC2 instances go down, but you pay for and keep S3, Dynamo, etc. At least enough to salvage or implement a contingency. You'd still owe Amazon the money.

It's tempting to wonder why Amazon would incur that risk, but it is a risk already inherent to their post-pay model, and it serves as good faith mitigation to the runaway cost risk that is currently borne by the customer.

Not perfect, but maybe a compromise.