Each platform has different requirements for their username and certain usernames are alewady taken.
This is why you will need to have 2 OnlyFans accounts.
You can reach out to these pages and ask if they do Shoutout For Shoutout S4S or if they offer a paid shoutout service.
The only way to do this without promotion on social media is to promote on the OnlyFans platform itself.
Very often you will find cross-promotions to other free accounts.
You can out these accounts too, and the other accounts that they are cross-promoting, and so on.