Thank you for reaching out with this question. I don't have experience cleaning stored pollen out of combs. The only successful way I've heard from other beekeepers is what you described in terms of soaking and spraying frames. I understand this process can be time consuming and messy.

Normally I've culled old frames from MSU hives by discarding entire frames or replacing the comb with new sheets of foundation.

One point that you may want to consider is that beeswax tends to absorb and bind to pesticides that are brought into the hive. There are questions about how exactly pesticides in wax affect the colony. Discarding frames may be a way to reduce pesticides in the hive, especially if they were used for several years.

Happy beekeeping!