Contact your MSM and feature request it; if you still that benefit that is, per rumor.
Meanwhile you should wish for a million apps to even be a possibility, otherwise this is what happens: inflexibility and process deadfalls when there is no api/apps allowed to tailor a site to need.
The current new account system doesn’t allow apps or liquid modifications.
And b2b is documented as only working with the new customer account system.
So until they decide to realize what a fundamental process problem this is for B2B, the approval process needs to be an offsite roundabout ?.
Of course if a B2B prospect lands on the dedicated store how do you even communicate to them where they should go to apply? ← And isn’t that the real fundamental problem buried in the middle making this process broken, there’s no way/where to put business messaging for new systems login pages, can’t even add a link; like how you could customize a themes password page when locking the storefront.
For some sort of messaging on the B2B sites , you could put a link/qr-code within the logo image to be displayed via the branding settings that may show in that area.
Otherwise have to treat the B2B url like a badly kept secret, anyone might know but everyone that’s supposed to know it should know they had to sign up on the main-site first.
With the clunkier alternative being don’t restrict access, then use an access control app like locksmith or theme customizations to lock down all/parts of the B2B site for only approved accounts since anyone can make an account /ugh.
Classic and new account types
https://help.shopify.com/en/manual/customers/customer-accounts
Also see new customer login url sharing:
https://help.shopify.com/en/manual/b2b/b2b-customers#customize-notification
Good Hunting.