I saw a company pay $30K for 5 days access to a similar service.
Bootstrap the service by using this script under the hood and improve it overtime: https://github.com/newsapps/beeswithmachineguns
Use your $100K credit for spawning instance but also as a marketing hook: "first 1 day free!"
Try to build any product that offers larger amount of free evaluation period.
If before 1 year, you have $paid_customers > 100.000, continue, go on, otherwise, just kill it.
Also there is more services in AWS, than EC2 and S3.
Only exploring them gives plenty of ideas... machine learning, transcoding, no- and sql scalable databases, mailing or dns services, world-wide advanced networking and delivery, etc, etc, etc... on an scalable and elastic way, high composability and awesome APIs and docs.
wtf, even you can use that money on yourself, purpose it for your own self-learning of AWS... put your $idea on world-wide high availability, automating all the AWS integrable components, and provision it thinking about time zones and world-wide timezones, usage peaks, etc.
Any ideas related to social-network-effect, or massive concurrency, are nice with an "elastic" architecture. For example, build a game that you can play from different social networks!
Last, if you're free to choose where the money goes, in your situation I could donate a some part, to my favorite opensource projects and supporters. Should feel good.
Do you know what features this service had that made it worth $30k for 5 days access? Did they have some unique and useful features, or was it more about the available bandwidth/RPS that could be generated?
Enterprise pays a boat-load to HP and others for performance/load/stress testing. Someone needs to figure out how to offer serious performance testing at an affordable price.