I'm curious if there are any examples in poetry of the word previously being contracted to three syllables, by contracting it to prev'ously, or some variant spelling. It would seem that we are keeping the v consonant but eliminating the i sound. Is this ever done?
After checking the OED, Google Books, poetryfoundation.org (via Google), and EEBO, I was not able to find any examples of prev’ously. I was able to find just one example of prev’ous though (making it extremely rare):
While Turks and Pagans, and the stubborn Jews,
Had something ￼ prev'ous, helping them to chuse:
The last, their Circumcision had before,
And learnt only one Deity t'adore,
This source is old, and it has many examples of what I would describe as over-the-top use of apostrophes (such as o'th', w'Examples, and liv'd & dy'd, and liv'd) so I would not really suggest emulating it.