You can have a fascination with opiates. But you really don't need to jump to IV. You could plug the morphine. Its got a good bioavailability, I believe in the 90% range.
If you ain't got much IV experience and nobody around to guide you, you could kill your veins in no time. Also IV opiate use is in my view a different kettle of fish to other ways of 'consuming' them.
However if you are set on doing it, then BL has advice on how to IV. Try YouTube as well. Get as much Harm Reduction advice as you can. And obviously go to a Pharmacy and get a swab pack, and remember only use a needle once.
Keep your dosing low as possible, I'd your opiate naive its obviously really easy to OD. If I were you I would go for 1-2 mg no more, you have 70mg so start nice and safe. Its IV so its an instant hit, so whilst people who first take codeine should start on 60mg, 2mg IV would be about 40mg codeine, but the this is IV so it will hit you within seconds. Start SLOW
But please think about plugging. (Up the bum). But still stick to only 1-2mg you have 70mg to play with. If its doesn't do much then you can increase by 1mg remember if you take 2mg then do 4mg next time you are doubling your dose, obvious but crucial to avoided to OD,
Please don't IV! But if you do get as much HR as you can