If you are using the type of mechanicals that swing open on impact (such as a wasp jackhammer like i used to shoot), I would simply wrap the closed broadhead with dental floss where my rubber band would normally go. Wrap them good and this way when the broadhead strikes the target it doesn't open at all. Just pull them back out like feild points and shoot again and your blades will still be sharp. I think you'll find after a couple shots though, that your mechanicals will be shooting right with your FPs and there's really no need to shoot them anymore than you have to.