It's said that EEA countries outside the EU could 'unilaterally' apply some kind of emergency brake to curb immigration, and they cite Article 112 of the EEA Agreement.
Unfortunately, no they can't. As a member of the EEA outside the EU we would be bound by the EJC decisions rather than the EEC, but one of the EJC's primary roles is to ensure consistency on how the EEA Agreement is implemented with regard to EU countries. The EJC are going to use the same criteria on whether our safeguards are acceptable as the EEC for that reason. If they don't agree on our curbs, they'll refer it to arbitration and possibly ultimately the European Court of Justice.
The question has to be asked, since even EU countries are signatories to the EEA Agreement and therefore so are we, why haven't we taken the arbitration or ECJ route already? Could it be that the EEC have rejected our claim that we could apply safeguards, and any legal challenge would fail because the ECJ would uphold the EEC's decision?
Any arguments that say that we have some kind of immigration control while being out of the EU while a member of the EEA are fundamentally flawed.