We had the same problem and were able to solve it by setting up a syringe pump with the tubing taped to the objective to slowly replace water as it evaporates. Maybe something like that could work?

Seeing a project published can easily make you forget about all the sleepless nights, frustrating days and the many failures along the way. We highlight some of this "invisible" part of our journey in a behind the paper blog post here: microbiologycommunity.nature.com/posts/more-t...