Hello,
You can only do this if your EM simulator accepts 3D dielectrics, as the dielectric in the coaxial cable is different from that of air.
You may that a coaxial cable has two independent circuits: the differential mode circuit and the common mode circuit.
The DM mode circuit is the current in the center conductor and a same but opposite current at the innerside of the braid/shield.
The CM mode circuit is formed via the current at the outside of the braid/shield.
You can simulate your setup in two steps. Draw the dipole and draw the screen of the coaxial cable. Replace the inner circuit of the coaxial cable with a localized source directly at the antenna. So the source is connected directly between the dipole halves. Note that the braid of the coaxial cable is connected to one of the dipole halves and you don''t draw the inner conductor.
Run the simulation and see what happens (look at the current distribution and modify the coaxial braid length).
Once you have S11 for this arrangement, put this in another (circuit) simulation to take into account the effect of the coaxial cable electrical length and loss. If the cable's characteristic impedance is same as the reference impedance, it is relatively simple as you only get a rotation of the S11 graph (when in Smith Chart plot mode) and some scaling due to cable loss.
You probably can't simulate a sleeve dipole when you can't have 3D dielectrics. The dielectric is inbetween the sleeve and the coaxial cable.