Technique to be swallowed up by Lakiora

lol not sure, but if you attack at the left side near his neck he might. I've gotten swallowed like 5 times in one game, not sure if that's what causes it.

you say the left side looking at the Lakiora, or the left side riding the Lakiora?
When you have been eaten by Lakiora 5 times, you were shooting it with the ballistas?

The host has the highest chance of getting eaten. This doesn't mean he won't go for someone else and half the time when he does eat someone else is because the host were in invulnerability frames. Another thing to rember you can't get eaten solo , so you would need at least one other person with you if you want to get the title in a easier way.
The 50~69 mission would be best if you're aiming for the title. Since one it's easier and two he doesn't make the boss room a venom factory.

how you deduce that the host is eaten more than once?

get a dood you can duo lv50 lako with
you both set up camp so you can get another buff when ur first one runs out
you will be able to get about 5 eats per run before the buffs run out
then leave party to do it again.
the eating anim happens about once every 4min (give or take 30sec)

got the title with the leather ruiner on the first day like this with my friend

If he does that swallow attack, the first one he hits get swallowed, that's how simple it is..

Tested this with a buddy did lvl 50 lako with him about 15-20 times? We both got titles.

Another thing i noticed is during the lvl70 version, if u stand to lakorias left(near his neck, not head) It almost always swallows me, even if im not host.

15 times o_o thats not to bad guess ill go get my title.