Woodpecker deterrent additive for plaster finish coat?

We are building our house and have a lime plaster scratch coat over earthbags filled with scoria. We can get occupancy permit with just the scratch coat done (after we finish the rest of the house, that is).

Problem is, a northern flicker is trying to nest in those scoria walls. By the time we realized it, it had broken through the lime plaster, and removed over a gallon of scoria, almost all the way through the earthbag.

We repaired that hole, and the next day it had tried to start two others -- luckily in an area reinforced with wire mesh where the bags connect to the roof, so it didnt get far. For now we strung some old CDs in the area as a scarewoodpecker, and it seems to be working OK to keep them away, but it isn't a long-term fix.

So then we were wondering if we have to wire mesh the whole wall before the final plaster coats... super expensive, a pain in the neck, and not effective since they still damage the plaster before hitting the wire.

A quick Google search indicated there is a paint-on coating used to deter woodpeckers from the new synthetic stucco, using similar chemicals to nail-biting deterrents for kids.

We don't want a paint-on coating, but thought maybe we could find a similar non-toxic additive to incorporate into our finish coat.

We will keep looking into this, but I thought I'd give a quick shout here in case anyone has done this? Anyone know what material to use and availability? Have any of you done this with a final plaster coat to good effect?