Soaking mussel in fish oil seems counter productive as the fish oil is likely to attract different fish than just the mussel scent unless you are using the mussel pieces as flesh and not for the inherent mussel scent. But it is an interesting idea.

I chatted with an old (Ancient) Greek guy earlier this year who swore by using squid as bait.
However he kept it in a jar of olive oil and that was the point of difference in his mind.

Either way, It's good to have different ideas thrown up and discussed. Keeps the mind active and promotes evolution.