I think I'd simply budget for it. Treat it as part of the sales process.

Using a Saas example... most companies end the 'sales' or acquisition cycle when the customer pays their first monthly subscription fee.

I'd go so far as including this onboarding process as part of the sales cycle. Even if they're paid, they're not a customer unless they've been onboarded.

Scaling this is tough. But I think as acquisition costs continue to rise, it'll just be an expense that you're happy to take on the chin because of how it has a direct relation with LTV of the customer.

If you've got a Saas app charging $29 a month, then theoretically a 15min to half an onboarding call pays itself back if the customer even stays on for one month longer than they would have without it.