You have to compromise I'm afraid as the LS35 only has one RGB scart. If you had more than one RGB scart, then you could have separate RGB centring settings for each scart socket and it would remember them (as is the case on the LS60).
If you remember your settings though, you'll soon be adjusting the RGB Centring value in the blink of an eye each time you switch between PS2, Sky and DVD
It probably happens with DVDs and other inputs in WIDE mode, just that you haven't noticed it yet. You will always get a little minor bending on widescreen CRTs (horizontal and/or vertical) - 1 cm doesn't sound too bad. You won't be able to correct it in the service menu, as the service menu deals with vertical geometry settings (there are occassionally a couple of horizontal geometry settings in Sony service menus, but they deal with horizontal trapezoid settings, not this sort of problem).