Ok this cheat is only for the ones which have seen latios/latias and have escaped.All you have to do is keep going town to town(I mean suppose it is next to pacifidlog then go there)and see in the pokedex again if it is there,where you are then use any repel(I recommend you to use it before) and then use a pokemon with sweet scent.e.g.masquerein.But that is not it it may flee again all you have to do is catch a sableye and lvl up to 56 or above(I dont know what lvl but it should be 56 above)then keep it in front of ur party because it has mean look and also no attacks are effective because it is a ghost and dark type and latios/latias has only attacks which are phychic and normal.I'll give you what attacks it has
Latios
Lusture purge(psychic)
Psychic(psychic)
Protect(normal)
Refresh(normal)

Latias
Mist ball(psychic)
Psychic(psychic)
Protect(normal)
Refresh(normal)

I recommend you to use knock off 4 times with sableye to make his health less(If you are catching latios/latias at lvl 56)
Hope I helped