Doesn't work. Those who have the hope purify themselves as that one, i.e., Christ, is pure. That one refers back to him.
And everyone who has this hope in him purifies himself as that one is pure. 1 John 3:3
G1565 ἐκεῖνος ekeinos (ek-ei`-nos) p/d.
1. that one
2. (neuter) that thing