Say: you have two weeks to submit any requests. After that, everything gets released. It's your trade secrets after all.
If someone actually wants to understand how/why the vaccine was approved, the most sensible option IMO would be to tailor the FOIA Request more narrowly. Request the summary section: it should lay out the rationale, without diving into specific details that might need redaction. The only other alternatives I see are lobbying congress to either a) allocate more money for FOIA or b) make some categories/documents releasable as-is.
OTOH, asking for a third of a million pages--many of which no one has real intention of reading--does seem like a good publicity stunt.
[0] If participating in a clinical trial gets (potentially embarrassing) personal details leaked, we won't have nearly as many volunteers next time.
An alternative is of course that we would treat requests by multiple people as more important, for example, if we assume that 1000 people requested these documents it would only take less than a month, but imho that's a huge slippery slope where information can effectively be hidden by inflating the size of it.