Here's a few things I've done for B2B engagement with a startup.

1. Engage with their primary IT services/solutions vendor for a three-way deal that commits the vendors support for your product for a 3-5 year timeframe - This will mean a margin erosion, but you'll benefit from having a larger partner and the execs will be comforted by the fact that there's a longer term support vision.
2. Put your code and design in escrow - There are many source code escrow options and you should negotiate the contracts carefully and with good legal advise.
3. Build your pricing mechanism in ways that stagger/cycle payments over a longer period of time - This is tougher when you are starting up, but it maybe a point on the negotiating block that will help the vendor managers/contract teams lean towards you.

Your 'Go To Market' strategy should envision as many scenarios as possible and build a response case around each. There is no single silver bullet that will convince all execs who deal with startups.