1D and 2D size optimization - second order elements

Hello,

I am running a size optimization on a Model containing 1D and Shell elements.  The 2D mesh is very rough so that the  relation of cross section to 1D element length is not too bad. I would like to use second order 1D and 2D elements in order to improve the stress results. Is it not possible to  use second order beam elements in Optistruct?

If not, is there another solution to connect shell mesh to 1D beam elements which allows for different element sizes?