For thickening, you could try Cream of Rice porridge for breakfast. I make it with Coconut milk and cinnamon and add in mashed bananas, which also help thicken output and sweeten the rice porridge. And both the Coconut Milk and banana add calories and nutrients. Could also stir in smooth peanut butter.
White sushi rice with meals is a big help. For extra nutrients, protein and calories, put a couple fried eggs over a bowl of white rice and flavor with a bit of soy sauce and sesame oil.
Peanut butter and almond butter are good for thickening and for weight gain / extra calories without sugar. I made almond butter in my food processor.
You might also try taking Apple Pectin with meals. Just be careful of taking full capsules - my first and only time taking one it seemed to get stuck in the stoma and cause a blockage and mess. Maybe try opening the capsule and sprinkling the powder on your food or trying a different form of Apple Pectin.
Pasta (regular and gluten free) might help as well.
Gluten free breads made with rice flour may also help. Basically, rice works well and you can seek out different forms of it to add in to your diet.
You could dilute Ensure with unsweetened Almond Milk to cut the sugar, but I found Ensure to cause gas and diarrhea.
Starchy vegetables other than potatoes might help (or hurt), such as winter squash, specifically Kabocha or Jap pumpkim.
Maybe eating slowly and small frequent meals/snacks might help - at least control the flow of output if not the consistency. Also, avoiding drinking beverages with meals and instead sipping between meals. If you have a lot of liquid output, you might also be at risk of dehydration/electrolyte loss. You could add a pinch of salt (small amount is tasteless) to your water to help counter this.
Good luck!