You can inject crack but you gotta bend it over, fuck it in the ass, smack it around a little, and after some work you have something that, well, it will get you high but it's definitly not considered "harmless" (as you CAN be putting some bad shit into your body!) ..
But anyway, um, yeah, it's great that you actually NOD from codeine - hell, you might actually get insane from this combo.. generally you would take your narcotics first, wait until thats hitting you, then rail your line of meth (not a gagger, you don't want to totally overpower the narcotic effects, you just want to slightly negate it) .. if you wish to smoke the meth you can, but I don't recomend it .. I am sure someonep will ring it advising that you take the meth orally, however, I don't advise this as the codeine will wear off many, many hours before the meth will, and unless you plan to tripple dose you may find yourself suffering from the anxiety induced by the meth ..
In all honesty, it's not fair to even refer to CODEINE and METH a "speedball" .. you should at LEAST be dealing with hydrocodone, and even then... if you don't bang it at the same time, it ain't a speedball.. the idea is that you slam both at once, and it's THAT combo that produces the high we know as a "speedball" ..