Well you can still create shape files, compile them into shx files, and insert them into a linetype definition, you just have to do it the long way.
I like CAB's suggestion about using hte parenthesis rotated... that's probably the best K.I.S.S. method yet.
For example, it might be :
*WATER,Water Linetype UUUUUUUUUUU
A,.001,["(",STANDARD,S=1,R=90.0,X=0.001,Y=0.001]
I think lines have to start with a dash/dot of some kind, not sure. You could try adding the above two lines into your .lin file and see what happens. If it appears upside down, either use the other parenthesis, or change R=90.0 to R=270.0. One or the other.