You just leave the 4 plants around the exit to UT alive, then you let them hit you over and over until your chest has red lines on it. Go up and run around until your HP recovers to pink chest, then repeat.

Many people prefer to relocate Jenny instead, so that there's a steady supply of plants to train on.

Also, there's the matter of food which, since you can't kill any plants for kiwis, is limited to that which you can kill on the level below. As chao mentions, better to just teleport Jenny away and get a constant stream of plants with yummy fruit on their bodies.

Training End that way in CVS will cause to many scars that would decrease HP and other stats. Eat some spiders or get bitten by a snake at 64 or more HP.

It occurs to me another method could be to wear Armor of Great Health (with some enchantments, probably) and then get poisoned repeatedly. Perhaps by drinking poison, if you have enough END at that point.

empty cans, mellis, schoolfood, seges...........
the sky is the limit but keep you HP under 400 if you don't want to fight Ischaldir

A nice way to train your endurance is taking two broken bottles to New Attnam, drop one next to the other a few tiles away from where you appear when entering the village, unequip yourself and walk on them. When one of your legs get hurt past the red display equip your boot so you don't lose the limb. When both your legs are quite hurt you go to the wilderness and run until you heal. With this method you can boost your endurance considerably and if you get hungry you can kick bananas from the platform where the banana growers drop them and then eat them.

Try to leave all your stuff in some of the houses and lock the door so you don't go burdened when your legs are hurt as you Lstr will drop.

I don't suppose you could also SoCM a large chest into schoolfood and treat yourself to a vomit fest?

The secret of the school food is to eat it in the wilderness, because you can't vomit there. So you just run around until the poison goes away.