It wouldn't be a boss question if we didn't include TibiaBosses in our answers as a resource. This goes out to Williams as the credit goes to him when it comes to the article and boss answer. The answer to your question is yes it's possible to lure the Spawns of the Welter south of the cave to avoid them healing the boss! Just make sure you kill the eggs to avoid this as well.
Killing Welter solo - Elite Knight by Williams
.....You need to remember that those spawns heal themselves and that Welter can devour them to heal himself. It's important to get rid of them before we start killing the boss.
I destroyed the egg which was blocking my way and quickly lured the Welter south of the cave. Then I could kill the spawns and destroy the eggs without any problems.
With spawns and eggs cleared we can proceed to slowly lure the boss near the stairs.
It's actually the easiest part now. We need to kill the boss with the usual chain of spells (exori gran, exori min, exori, exori gran ico, etc.)
Welter heals much and quite often so try to do it as fast as possible. Whenever an egg appears, move with boss to stand next to the egg, so you will destroy eggs and kill boss at the same time. Don't let the spawn to hatch, because things might get hard.
And the final hint - remember to look before you leap. If you go down the stairs and see the welter with for example 7 spawns it will be extremaly hard to use tactic described above. Don't get yourself surrounded by hydras/spawns.
However if your level is 400+ you can try to use utito tempo+spells while going up and down the stairs. This should be enough to kill spawns with 2 or 3 hits (spawns have about 2k hp). Then you can skip the luring and just proceed with killing the boss and destroying eggs.
Also for here is another video of a team doing it
In this video there was a team (a mage and knight) whom at 3 minutes you can see the Spawn of Welters and how bad it can get, however they eventually lured them south to work with the boss himself - the Welter. Each time an egg appears they kill it. The mage is sding and the knight is tanking at times.