Here are all the middle names used for Felix found on the 1911 England and Wales census and cross-referenced with the CRB.
Felix Aaron
Felix Adolphus
Felix Agrippa
Felix Alan
Felix Albert
Felix Alexander
Felix Alexander Hugh
Felix Alexander Vincent
Felix Alexis Armand
Felix Alfred
Felix Algernon Orlando
Felix Alonzo
Felix Aloysius
Felix Alphonso
Felix Ambrose
Felix Amos
Felix Andrew
Felix Anthony
Felix Archibald
Felix Arthur
Felix Aubrey
Felix August
Felix Augustine
Felix Augustus
Felix Austin
Felix Barnaby
Felix Benedict
Felix Benjamin
Felix Bernard
Felix Bertie
Felix Bertram
Felix Boris Paul
Felix Charles
Felix Chester
Felix Christopher
Felix Claude
Felix Clement Vincent
Felix Clifford
Felix Cornelius
Felix Cuthbert
Felix Cyril
Felix Daniel
Felix Daryl
Felix David
Felix Dionysius
Felix Donald
Felix Dominique
Felix Duncan
Felix Edgar
Felix Edgar Horatius
Felix Edmond
Felix Edward
Felix Edwin
Felix Eli
Felix Elias
Felix Elijah
Felix Elliott
Felix Emmanuel
Felix Emile
Felix Ephraim
Felix Erick
Felix Ernest
Felix Ernst
Felix Esau
Felix Eugene
Felix Eustace
Felix Fabian
Felix Ferdinand
Felix Finbar
Felix Francis
Felix Frank
Felix Frederick
Felix Gabriel
Felix Geoffrey
Felix George
Felix Gerard
Felix Gilbert
Felix Gordon
Felix Gregory
Felix Guy
Felix Harold
Felix Harry
Felix Hector
Felix Henry
Felix Henry Gustave
Felix Herbert
Felix Horace
Felix Horatio
Felix Hugh
Felix Ivan
Felix Ivor
Felix James
Felix Jarold
Feliz Jason
Felix Jocelyn
Felix John
Felix Joseph
Felix Josiah
Felix Joyce
Felix Jubilee
Felix Jules
Felix Julien
Felix Justin
Felix Lancelot
Felix Leo
Felix Leon
Felix Leonard
Felix Leopold
Felix Leslie
Felix Lewis
Felix Lionel
Felix Llewelyn Ellis
Felix Lloyd
Felix Louis
Felix Lucien
Felix Malachy
Felix Malcolm
Felix Marmaduke
Felix Martin
Felix Maximilian
Felix Merlin
Felix Micaiah
Felix Montague
Felix Mortimer
Felix Nathaniel
Felix Noel
Felix Norman
Felix Oliver
Felix Oriel
Felix Orlando
Felix Oswald
Felix Oswald Leonard
Felix Otto
Felix Owen
Felix Patrick
Felix Patrick Raphael
Felix Paul
Felix Percival
Felix Percy
Felix Peter
Felix Philip
Felix Pius
Felix Ralph
Felix Randolph
Felix Raymond
Felix Reginald
Felix Reuben
Felix Richard
Felix Robert
Felix Romeo
Felix Rufus
Felix Russell
Felix Samuel
Felix Sebastian
Felix Septimus
Felix Sidney
Felix Stanley
Feliz Stephen John
Felix Theodore
Felix Thomas
Felix Timothy
Felix Valentine
Felix Victor
Felix Vincent
Felix Vivian
Felix Wallace
Felix Walter
Felix Walter Theophilus
Felix William
Felix William Henry