Salvete!
I have found that expression in this passage of Alvarez’s De Institutione Grammatica:
Illinc [in rationem viamque tradendo qua Latinam Linguam discas] omnia quae potius impedimento quam emolumento esse possunt, omnino, quoad ejus fieri poterit, removenda sunt. (De Nominum Declinatione, 3.)
Lewis and Short says it means “as far as possible“; why is that “ejus” used? “Quoad fieri poterit“ would literally be “as far as it can be made“, which makes sense, but that “ejus“ does not seem to refer to anything previously mentioned.
Bene valete!