I've never IVed cocaine but I watched a guy do it one night. Trust me. No amount of weed is going to "ruin" the effects of IV cocaine.
If you've never IVed cocaine before I highly advise you do not go through with hit. You will be tempted to hit yourself over and over again in a very short period of time. My friend said it wasn't even worth doing unless he did it as a speedball or had hydromorphone to mix in the shots. But opioids were his drug of choice you might feel different on this issue.
He told me it was all rush and hardly any legs with cocaine IV. If you snort it at least you get 15 minutes or so before you desire the redose. My friend was prepping shots the moment he got done pushing the last. I watched him go through a gram of bomb cocaine (I snorted some) in the span of like 1-1.5 hours or something like that. He ran out of veins and boofed a syringe full of cocaine water and his own blood in the middle somewhere. Bent right over in front of me. Then he started prepping his next shot for injection.
Guy used the needle a lot around me and I never seen him do anything like that with other drugs. Even the IV hydromorphone he could hold off for awhile. Cocaine made him go full retard.
Edit: Just noticed OP is months old and thread was recently bumped. Oh well. Maybe this will help someone in the future.