Last year, the House of Lords recommended Ireland and Britain negotiate a draft bilateral agreement. The Irish Minister for Finance rejected this, stating that UK would have to negotiate with the EU.
But there was a precedent for bilateral Irish / British negotiations on trade. In 2013, both governments signed a Memorandum of Understanding for the export of wind energy from Ireland to the UK. In effect, a trade agreement. The Greens lost the following election in the UK and the agreement ultimately never proceeded due to lack of political will, not because of any procedural issues.
It seems when it comes to wind energy, there are no rules or procedures. All that is required is the political will.