This problem occurred with one of my players. They wanted to play a druid figure. Everything fit, except that the druid did not use a wild form, the character had a kind of "this form was given to me by nature, why should I want to change?" Mentality and he was more likely to be a summoner and someone who would communicate with ghosts. I thought it was cool and went with it.
But there was the problem with a druid key mechanic, Wild Shape. The character never used it, so we tried to give the druid some kind of replacement.
In the end I gave him the opportunity to burn his "wild form" to keep a concentration of a single spell …
It turns out that the ability to use two spells with concentration really makes OP.
I would like to ask if you know how this could be balanced. And if you know other valid Wild Shape substitutions.
I thought I could use the wild form to maintain concentration if the druid does not pass the con-check. I'm not sure if that would be balanced. Another option was to bring ReSpec to the Cleric and give him the Druid Spell List instead of the Cleric List. But that did not fit the character.