Salaamalaykum waa rahmatullahi brothers,
I second the advise of most of the people to reallocate time from leisure activities to ibadah during Ramadan. I too have planned to cut down on some of my own activities during this Ramadan InshaAllah.
Also, you could focus on an aspect of your physical training that doesn't involve dehydrating to a great extent. I would suggest 'flexibility training'. It is often overlooked completely by non-athletes who train. Yet it is beneficial for the joints and muscles in your body and is essential part of strength training.
You could try out some static flexibility exercises, they hardly involve a lot of perspiration.
PS Muslims have a head start on their back bones & knee joint stretches as we perform rukoo number of times a day (as well as sujood). Bending and touching your toes ? Should be a piece of cake for all of us.