I know i'm not a ds4 player but I hope I can still give some advice lol
I guess i'd just recommend using the playrecord function and then going to a section in a song where a split hold opportunity is present. Then just keep practicing and building muscle memory for doing the motion until you can start doing them consistently. Or even just go to a quad max and practice splitting that.
Feel free to @/contact me on discord, I can give you more tips/examples there
if you want to use ds4 to split holds, i suggest you use joy to key set △ 口XO to L1 R1 L2 R2 for exampe, my ds4 setting is: L1:口 R1:O L2:X R2:△ if i want to split △口 to △ → 口 , i will press △ → L1, or use my finger wipe △ → 口 of course you must spend a lot of time to practice it