SOYLENTCOMMUNITY1 is perpetual, or at least it's worked for me on the same subscription multiple times.
Edit: Oops. Apparently it works on the same account multiple times (intentionally?), but not on the same subscription. I could have sworn it did before, but it looks like I was charged full price on my last order. That was the first time I clicked the "Need more now?" button; it's odd that the easy option (clicking that button) is more expensive than creating a new subscription, which isn't burdensome or anything but kind of unexpected.