I waited for one of the pianists in the group to answer your question, but , allas, in the smoke of the flame wars, none of them saw the question.
First there is no way to help acquiring 'left hand dexterity':
dexterity Dex*ter'i*ty, n. [L. dexteritas, fr. dexter: cf. F. dext['e]rit['e] - Right-handedness. (
(Obviously I choosed the 'right' definition amongst others)
Second, I am obsessed with the same problem. It is known that Czerny exercises are mostly 'right-handed' . Hanon practiced with both hands does not help either - the right hand leads the left hand. Moreover, unless the exercises are mirrored (as in Schmitt) , the left hand does not get the fair treatement the right one does - but as the piano is built as it is, we don't have many choices.
So... what I can do is to give the right hand a day or two off, and play with the left one alone. Sorry for the bad taste, but sometime I imagine that I'm left with the left hand only and try to do every thing with it : open bottle caps - feasible, tie the shoe laces - unfeasible. Even if the left hand keeps up with the right one (in some parallel exercises like Hanon) I don't feel it 'at ease' and completely relaxed. So I play left hand only, very, VERY slowly, monitoring the 'relaxation' of each finger after he finished his 'job'. I constantly compare the relaxed feeling of the right hand and try to duplicate it in the left one. In fast passages the left hand tends to get very tensed and, eventually, stops to react (gets 'cramped'

. So far, I could not find any other way except playin a lot, slow, for extended periods, with the left hand alone. Do whatever you are inclined to do with the right hand - as playing by ear some tune - with the left hand. As 'Marbeth' said, get control - the speed will follow.
An easy way to watch for the left hand is to do the 'boring' exercises (Hanon, Schmitt) each measure first with the RH and then 'replying' to it with the LH. Also try to modify the 'rhythmic' patterns : dotted sixteenth at RH (lagging the second note) while LH plays normally and THEN try to do it with the LH while the right hand plays normally (an exercise in mental control). Or the RH playing twice as fast and then LH playing twice as fast as the Right. Any thing you can device to make left hand life misserable will probably help to get control over it (Just now, stop picking at your nose with the RH, use the LH - beware of that eye !)
And finally, give a Chopin Etudes recital at Pleyel Hall in Paris and keep us informed of the public response.
Good luck !