Great question. As you can imagine, many developers [understandably] share this pain. On our end it will unfortunately be a bit of an infrastructure journey before we can make a real sandbox happen.
In the short term, the not-ideal answer I can give is to
Use two (or more) accounts and pledge to yourself
Set the campaign to “per post” so the fake patrons don’t actually get charged
Not the best answer - take solace in that you’re not the only one with the pains.