Personally, I've dabbled in translating the lyrics to the Beatles' "Let It Be." The best I could come up with is "Estu ĝi," partly because it makes it clear it's not a direct command, and partly because its rhythm matches nicely with "Let It Be":
Kiam mi trovas min en malbon-tempoj
Manjo panjo venas al mi,
Parolante saĝajn vortojn:
Estu ĝi.
Estu ĝi,
Estu ĝi,
Estu ĝi,
Estu ĝi.
Flustru saĝajn vortojn,
Estu ĝi.
EDIT:
I've been thinking about this, and if making it match the Beatles' songs' rhythm is not your concern, then I would use "Tio estu".
Why "tio" instead of "ĝi" (or nothing at all)? Because "ĝi" is often used for tangible objects (tangible nouns like books and forks), whereas "tio" is often used for thoughts or events.
For example, if I wanted to ask you if you saw a book, I might ask:
Ĉu vi vidis ĝin? (ĝin = forkon)
But if I wanted to ask you if you saw the book falling off the table, I would be more likely to ask:
Ĉu vi vidis tion? (tion = kiam la libro falis de la tablo)
So, in the end, I'd recommend "Estu ĝi" if you wanted to match the song, or "Tio estu" if you wanted a closer match to the idea behind "Let it be".
Another edit:
If you don't mind taking some artistic liberty on pronunciation, you could re-write "Estu tio" as "Estu ti'", which works nicely in the song:
Estu ti',
Estu ti',
Estu ti',
Estu ti'.
Flustru saĝajn vortojn,
Estu ti'.
The final "o" is replaced with an apostrophe, which is allowed under rules Zamenhof set up. However, "ti'" is likely to be misunderstood by many esperantists -- even native speakers -- so if that's something you want to avoid, here's something else you can try:
Use "Estu tio", but emphasize the "ti" part of "tio" and de-emphasize the "o" part, as if you were saying "Estu ti...(o)". That way the "ti" part matches up with the "be" (in "Let it be") and the "o" part, while still spoken, ends the sentence as the sentence trails off.