Vectors are no longer an array of vars, they are just structurally like one.
You MUST use x,y,z with Vectors in lite-c

BUT, you MIGHT be able to do it with (untested)
(bla->testvar)=((var*)testvec)[1];
if you REALLY want to add the extra typing....

You may also be able to use
function test(var* testvec, teststrukt* bla)
...
If the function isnt "overload"ed.

Neither of these ideas are tested.