Hi Meg - yes that might be a good compromise. I know that when you subscribe to a magazine you're usually asked if you'd be willing to make a donation as well. But I've never been asked to make a donation when submitting. Worth a try perhaps.
I know that I am in the very privileged position of not worrying about a small submission fee, but the alternative, that poetry mags will not be able to continue, seems worse. What about if mags started off by asking for a small amount if you are willing. I can see that they don't want to exclude good poets who are penniless.