You can create "health spikes" around your own side of the screen, if you switch your Pokemon the Pokemon that will be switched in gets a bit of healing, BUT THERE'RE THREE BUTS
1. Rapid Spin can remove it (d'uh) 2. It only works once, the health spikes are "consumed" after a switch 3. It only heals a little bit but can be applied up to 3 times before switching.
So like... let's say you have a Jirachi who's in a good position and will not take much damage, you may spent the next 3 turns to set up "Health Spike 3". Then when Jirachi is KO'ed or you simply switch your next Pokemon will receive a healing. The strength of the healing should be similar to the normal damage-spikes. Or 3 layers of health spikes should be equivalent to one wish. Because basically it is like a "stored wish for the next pokemon to switch in".
I think this would be the most balanced way since you can't "switch-heal-stall" since the health spikes are one-use only since they're consumed. And if you want an effective heal for your pokemon you have to spent a few rounds to set it up.
It would also be on par with wish in my opinion. Health Spikes would have the downside of needing up to 3 turns set up before giving off the same amount of healing as a wish. On the upside these healing-spikes will "wait" to be used when you send in a new pokemon and it is healed upon switching in. Wish on the other hand heals you a lot but only after the next turn. So if you use wish and switch you may won't survive your enemies attack in order to actually receive the healing of wish.
I dunno... in-battle healing without items shouldn't be made trivial.