I don't think "nominally" is an option. The opportunity for making a PPR election having been missed long ago, the only hope for acquiring PPR status would be by the "based on the facts" route, wouldn't it?
The "throughout" in (2) applies only if you want it to be automatically fully exempt. You can get partial exemption based on duration of "main residence" status. E.g. if you own a house for 10 years and use it as a holiday home for the first 5 and as a main home for the last 5, then half your gain would be exempt, and only the other half of your gain would go through the mill of taper relief etc.