Post a picture of the bottom of the action and maybe our gunsmiths will sound in. I don't think there's anything that can be done with the recoil lug shown in the photos. It does nothing to secure the action to the stock against the backwords force of recoil.
This stock is much different than my Tikka T3s. I'm eager to see a photo of the bottom of your Sako action, as the action sounds to be built just like my Tikka T3s with the slot to accept the recoil lug. Which in your case is not being utilized.
Post a photo of your action and see what Chad or the other smiths have to say.
Oh yeah, if the Beretta folks disassembled your gun twice now, then they either forgot to install the recoil lug, or they never noticed the recoil lug was missing. There's got to be something missing that is supposed to engage the slot cut into the bottom of the receiver.
Either way, it looks like a thumbs down for Beretta/Sako on their rifle inspection and return process. They need to send you a functional recoil lug. I don't know if I'd send it to them again... they might forget to install the barrelled action in the stock before returning it...