Macgeek has another video in his continuing series of using Suica Apple Pay without credit cards. This one details using a JCB branded Line Pay pre-paid card bought at a Japanese convenience store and registering the card in the Suica app.
Apple Pay Japan does not accept pre-paid cards issued from any Japanese credit card issuers but you can get around this using the credit card recharge feature in Suica app that bypasses Apple Pay and charges Suica Apple Pay directly.
I find the initial setup rather cumbersome, but this should be easy if you are a Line user and have enough Japanese ability to create a virtual Suica card and register the Line Pay Card information in the Suica app.