to be honest, connecting Paypal, Bank card payment accounts with someone's Fiverr account is not a good idea at all. everything can be compromised very easily.
I wonder how easy is that
very easily. because you can't do that in just connecting your paypal to fiverr or any website that has linked to paypal feature payment. Paypal does not work that way.
Besides you can pay only using paypal checkout without linking your paypal to fiverr.
Yes, you can just use your account instead of him on buying stuff there. But i see the only reason why op is doing this is because it will give his fiverr account a review from the seller (well, optional) and make his account more mature with at least one activity.
Plus new account (if ever his account is new) have some discount on its first purchase.