OH, if this works out for you, you might consider IM, however, it takes a couple hundred mg to get there, but you STAY there for an hour or so.
IM would my preferred preference, do you know the dose/kg and also the which form used? It seems inefficient, but the duration could be beneficial. DMT has always left me feeling just on the cusp of something, before tearing me away.
My only comparative would be ketamine IM/IV. IM is nice, gently coming on in around 5 minutes before being pulled into it. IV is like being shot out of a cannon, I can feel it coming by the time I'm half way though my shot, but I still have around 90 seconds after administration to settle down. Never holed with a needle left dangling from me.
My worry with IV DMT (it was the same with ketamine before I took the plunge though), was with the reports I read of it coming on far too quick to remove the needle. This turned out not to be the case for, so So based on that I would be willing to take the risk with DMT.
DMT fumarate dosage would differ from HCL, Citrate, Acetate dosages, and with a chemical thats pretty dose responsive, several mg's error could cause complications.
With ketamine IV, I would aim to get the dose dissolved into .5cc for faster administration (for IM I would use 1cc). With DMT, I would aim for .5cc again, using an LDS syringe if available.
Using lemon juice may cause further complications in Calculating dose (I don't know what impurities and potential contaminates are in the lemon juice). You can get Pharma grad citric acid from most needle exchange programs, and they're available online relatively cheaply.
Apply the acid slowly, until a solution is formed, Don't just dump the whole lot in. Dilute with saline (avoid solutions with preservatives, buffers etc. if possible)
I'd just like to point out that I have no experience with DMT via this ROA, and it's probably wise to take my comparison to Ketamine with a pinch of salt.
I would highly recommend the use of a micron filter though, if you can obtain them.
Bottom line. Calculate your dose. Halve it for your first trip. Prior to this, do a tester dose (<5mg) to check for problems, adverse reactions etc. Do as much research as you can, until you're comfortable you know EXACTLY how to approach it.
Then post the methodology you plan in detail, for people to advise on possible pitfalls, errors etc.