HPC access models: many nodes for short periods of time



How do other HPC clusters offer access to researchers with jobs that regularly require many nodes for short periods of time?

We offer:
1. a free tier model that provides up to 500,000 hours in a general access pool with lots of nodes, which can accommodate the bursty nature of these jobs well but only until they hit the 500,000 SU limit;
2. a paid condo model for researchers to purchase their own nodes for their exclusive access; the cost of purchasing many (20+) nodes is prohibitive, especially if they are not needed by the researcher most of the time.

Neither of these models seem like a good fit for researchers who need access to many nodes on a regular basis but only for short periods of time.

Does your institution have an option for researchers in this situation?