At one point in your stint at the radio station you should play one mix of Breaking Point, there are certainly enough to go around. Besides the Original, which I am sure we all can agree is quite awesome there is also the Shatter Mix, Circus Mix, A.E Jaded Remix, 'Bibo's Remix' and of course the oft maligned Braeking Piont.
From there there are a wide variety of covers of the various mixes. Standouts include the Halt Tanner version of the Original (normalize it before playing it) and the Galaco Engrish version of Shatter Mix.
I know you have been wanting to fill out your English song playlist, so at least you have some tracks in a language your listeners understand. Here is my (not so) short-list of English Language Vocaloid Originals:
I'llSeeU-P
I'll SeeU, Headline Love, Succubus, You And I'll Fly Away, Halloween Requiem, Last Dance
Puffihn
Sunset, Lonely Flight, Secret Space, Bad Guy, Only a Dream, Without Us
Gumbi500
Night Illusion, Song of a Shy Girl (Luka), Starlit Sunshine, One-Hit Revenge Game
Ms.Constantine
Fr@cture, Pitch Black Refrain (Big Al ver.), Once Before the Fall, Nomad, Ephesus
Baggagelizard
Ice Sculptures, Want, A Lazy Song
Vortex11316
Morning Light, Forever
ChaoFreak
Centrifugal Cindi
Honorable Mentions: Come On Me by Horizons-P, Theme of /jp/ by Anonymous, Speechless & Beat Beat, Tick Tick by Reso-Nation Collab.
Not a complete nor comprehensive listing, but these are the ones off the top of my head. Some are better than others, all could use a bit of normalization before airplay due to differing levels.
If they don't need to be Vocaloid originals I have an
entire playlist of Engloid Covers.