With the redesign of the PlayStation Store, which will be available at some point tomorrow, we will give the users the ability to recharge their wallet funds via PayPal.
At least in some countries like the UK has been introduced this payment method already on sonyentertainmentnetwork.com that you find under Account> Credit> recharging. It is expected that this will be implemented after the PlayStation Store and in other countries. At least it is a now much easier to go shopping in other PlayStation Store.
An official announcement on this is expected shortly.