A quick clarification on this:
A proxy vote – either given to an EC member or a completely different person speaking on your behalf – has to be approved by the committee. You can’t “appoint” someone, but you can request that the committee agrees to them speaking and voting on your behalf.
And for that reason, you can’t appoint a proxy to make up a quorum. If there is no quorum then the committee can’t vote on whether or not to accept the proxy.
FYI, the quorum is based on 50 percent of the numbers of members of the EC agreed upon at the last AGM. So, if an EC allows its numbers to get too low through resignations and the like, it may have trouble even reaching the quorum required to appoint new members (as it can do to fill vacancies).