If they're like other element bushings that I've seen...toss them and buy a better brand.
Otherwise...if they're a tight fit, take a punch or the end of an allen key that's just about the same size as the bushing and push it staight in. If they're pressed in cockeyed...they might bind the gear axels.
If they're really tight...a good wack with a hammer will do it..but be sure to support the other side of the mechbox shell or you'll warp the shell.
A bushing tool is the best and most consistent. I have two...the AI version (THANKS CARL!) and the Promethus one.
Best of luck,