As long as the two meetings are entirely separate and you have complied with all of the requirements for a committee meeting as set out in the standing orders, this could be an option. I am not aware of any legislative requirement for co-option to be a whole council function, although there is clearly a strong argument in favour of this, so if you are setting up a committee specifically for this purpose, you may wish to consider whole council minus one. Alternatively, why not simply call an extraordinary meeting of the council for this purpose?
One final thought. If you are asking potential candidates to stand up and deliver a rousing manifesto speech, be mindful of the fact that this may not be an essential requirement of the role of parish councillor. The best candidate might be the quiet one!