There are several “cheats” to get into it. If I had a Cam I could make a Tut but I will try to explain this as well as I can. (Keep in mind this does not replace being able to actually do the trick
Once you’re in a Trapeze, you can take your index finger on your throw hand and insert it between the strings on the Trapeze. So you finger is under the string attached to the Yo-Yo, but on top of the string the Yo-Yo is sitting on. Now separate your hands, and you should be in a Trapeze still, but it looks like you’ve made a Triangle. You can now swing the Yo-Yo out to the side and over your non-throw hand, once it’s over… BAM… you’re in Double of Nothing. (This may also help you get the “feel” of how it should land)
This is a Cheat and does not replace being able to land the trick normally. The thing to learn most about doing strings tricks from Trapeze, Double or Nothing or other like mounts, is to learn the feel of the string. When I do those it’s less about hand-eye coordination and more about feeling where the string is, where the Yo-Yo is heading, and where it’s going. It’s just something you learn to by the feel of the string and it’s tension on your fingers. It’s important while learning to also make sure your fingers stay in contact with the string as much as possible to learn this “feel” I’m describing.
You could also try and do it the Houdini Drop way (catching the string on the first time over with your thumb, and then the second time with your index finger before it lands). Some people I’ve talked to have had an easier time learning how to land it that way.