For Alipay at least, you can buy vouchers/gift card type things from convenience stores, small shops, possibly even post offices that have a code. You then can enter the code on the Alipay website and load the money into your account that way. There is a 1% handling fee.

I don't think there is a similar method for Wechat. Of course, you can just pay cash to someone and get them to directly transfer money from them to you, which works for either app. Less messy than the Alipay voucher method as long as that person is trustworthy and comfortable with it.