This is an excellent question, but I am afraid that the answers you have been receiving have been in your best medical interest. True, Lithium carbonate does not contain any addictive substances and therefore withdrawal should be relatively smooth. Still, because of your lifelong history with bipolarity, the eased titration is beneficial because it will scratch the surface of the manic symptoms rather than flood you with them. Sleeplessness is typically the first indicator of mania's return, at which case a different medication may need to be substituted for the Lithium.
Too, long-term effects of lithium treatment are not nearly as noxious as long term treatment with atypical anti-psychotics for bipolarity, so if there is no Lithium toxicity, then it will remain the treatment of choice.
Anyway, I think your actual "withdrawal" should be reasonably painless - but I would be very hesitant to advise you to pursue this route without the supervision of your physician. And look at it this way, if you goal is to come off of the medicine anyway, and you have been on the med for quite some time, what difference does it make if you titrate in a day or a month? Two months? A year? In other words, you will eventually come off of the medication regardless of how you choose to do it, so why not take the safe road instead of a riskier one? Heck, if your goal is long term health (your reason for wanting less medication rather than more - which I wholly support), then why take a chance with your health in the short run?
My two cents. As always, you are advised to consult with the prescribing physician before making any decisions regarding medication. I wish you well though! If you are satisfied with the response, please hit "Accept." That is the only way I can receive credit for my answer. Thanks-