Can't remember the detail of the antiroll bar mounting but just a point about Elise/ Exige chassis. One of the main points of the glued chassis construction was that it allowed the use of a a high strength aluminium alloy which was NOT weldable as it is precipitation hardened. If this is welded, it WILL crack.
The chassis is mostly made of 6063-T6511 aluminium...that is very weldable. The only part of the chassis that is not 6063 is the floor pan, that is made from recycled aluminium, I think that is weldable also, but not sure.
The minor problem with welding 6063-T6511 is that there is no way to reheat treat the welded chassis member after welding. The good point is that it will work harden and age harden on its own and have equivalent/similar strength after some time if it does not fail before then.
The biggest problem with welding a bonded aluminium structure is that it will destroy the adhesive in the area. Since aluminium conducts heat very well, that heat effected zone can be quite large.
The great design feature of the bonded aluminium structure that Lotus came up with is that you don't get the stress concentration points around a weld, because there are no welds and the bonds have a very large surface area to distribute the loads from one member to the next. So, instead of getting a stress concentration area around a weld, the loads are distributed very nicely through the large area of the bonded joint. The one problem they had to overcome is the tendancy of bonded joints to peal apart under cyclic impact loading. That is the purpose of the 4 corner rivets on each joint; to prevent the bonded joint from starting to peal apart.
So, yes, the bonded aluminium Lotus chassis cannot be welded because of the adhesive, not because of the aluminium alloy. Heat treatment is another concern.