Hymns that Don't Quite Fit the Metre

[FrGareth]

Ah! It's Advent again, so out comes the Alma for the end of Compline, at least in my own personal devotions (no public Compline in my parish).

The Breviary offers a 10.10.10.10.10.10 English translation... with only one snag. The last line is "Thou Virgin first and last, let us thy mercy see" which to my limited powers of mathematics appears to have 12 syllables, suggesting that maybe I should drop the "let us".

And a few weeks ago, it was All Saints' Day, when the office hymn was "O Fair is Our Lord's Own City". It works brilliantly to the tune of The Church's One Foundation - but only if you omit the initial "O"!

Am I missing some musical tricks which make these words singable to a regular meter? Or is my abbreviating the least worst option?