I'm not sure that it's "easy", but yes you can use Swap to get HP & MP growth more quickly.
Notes: - It only compares the start of battle HP/MP to the end of battle HP/MP, when it works out the chance of growth. So it doesn't matter how the HP/MP were lost during the battle. - Losing an amount over half their max-HP or max-MP, gives the greatest chance of the growth. - Running out of MP is the biggest problem of Swap, it can get very costly. - Your other party members will still try to resist Swap with their Magic Defence, when you try to Swap their HP/MP with the caster. ---