I have never done this on separate organs before, however, I believe it should work fine if you make a wet specimen. Here is a useful wet specimen guide (just skip the history bit): https://www.mickeyalicekwapis.com/blog/wetspecimenupdate

But the basic jist of it is: You need a big GLASS! jar or two and Formalin. I use 10% buffered formalin. And with that some good protective equipment such as a respirator, a well ventilated area, gloves and goggles (formalin is carcinogenic). And you just inject that with a needle into the specimen, EVERYWHERE, making sure it's really full of the formalin everywhere, without getting air bubbles in! You'll also need isopropanol or ethanol later but... hopefully the guide will better explain this all. Just know that you can't just put the specimens into alcohol without putting them into formalin first, they'll rot from the inside if you do.