It would appear to me that the story is the result of the "Irish Air Accident Investigation Unit (AAIU)" publishing their report on the incident, not such a slow news day that The Mail had to go did up a year-old story.
There is no mention of the Captain making any PAs asking for random passengers to come fly with him either... but it does seem reasonable that he would ask the cabin crew if there were any non-revving pilots on board, and finding that there was a FA with a Commercial ticket working the trip it would be prudent to have someone else strap in.

Lets see...
1. Incapacitated crewman.
2. Company employee joins captain in cockpit.
3. Divert to nearest suitable airport for medical attention.

Not really as exciting that way, but still covers all the salient facts.