So, right, there's an x-y problem in my question. The context is we have a couple hundred domains, packed into a few certs due to constraints of our LB setup; each month when the cached validations expire, the person adding a new domain waits on a bunch of domains to revalidate, and often has to retry the process a few times because of LE-side DNS errors (reasonably close to this description, FWIW: DNS problem - SERVFAIL for (seemingly) correctly replied names). The workaround I was considering was renewing our certs more often than expiry requires to have a chance of getting revalidation triggered by an automated process between the time the cache expires and the time a human wants to make cert changes.
The volume as well as content of replies make it amply clear the LE community does not consider early renewals a good idea. 
I've made some other changes on our side to try to make the ergonomics of the process a little less bad already and can think of others. At this point I don't expect a solution, but now you have more context.