You can do one-time donations via Liberapay. Just select the option to be reminded to renew instead of automatically renewing. You'll get an email that reminds you to renew when the time is up, but you can just ignore it.
Addendum: Yes we know that you think ml/hexbear/grad are tankies and or .world are a bunch of liberals but it gets old quickly. Try and come up with new material.
You can do one-time donations via Liberapay. Just select the option to be reminded to renew instead of automatically renewing. You'll get an email that reminds you to renew when the time is up, but you can just ignore it.