Impossible to finish Baldur's Gate 2 with a capped, solo mage without cheating? (Well...one cheat...an empty bag.) Not impossible. This is a path definitely not recommended for those too impatient to learn exactly what all those spells do, or suffer through some very slow battles, but I did it, so you could too. Remember always that your intelligence and wit will outdo the cruel, mechanical logic of your enemies every time, and you shall be victorious.
After finishing Baldur's Gate II with several different characters (twice solo with an elven Fighter/Mage/Thief exported from BG1) I thought that this would be the ultimate test of magery, game knowledge, patience and prowess...and was inspired to it after finding and exploring the powers and possibilities of the Staff Of The Magi, without which of course this would have been far more difficult or very nearly impossible.
Follow my journal with the links above, and I shall detail to you just what "impossible" means.