If they are not fully thawed he may be picking up the heat radiating from your hand. The organ they use to sense food focus's on heat...if you put your hand and a frozen thawed mouse in front of a snake, they will pick up the scent of a mouse and the heat on your hand and might bite you instead of the mouse. Tongs could help with this as they do not hold heat.
I wouldn't feed him in his cage either...then he starts to think anything that comes in his cage is 'food' and since you probably take him out to mess with him he might mistake your hand for food sooner or later.
Frozen/Thawed should be good in a freezer for 1 year if properly sealed. (zip locked).
I would get a tub to feed in. I feed all my snakes outside thier tanks/tubs and I have 9 of them, haha.