If you set the vpulse to toggle between -100 and +100 mV, this should fix the dc level.
For the modulation, you could put an ideal multiplier in the module:
Code:module mymod(pulse_in, sine_in, out);
inout pulse_in, sine_in, out;
electrical pulse_in, sine_in, out;
parameter real gain = 1000000000;
analog begin
V(out)<+ V(sine_in) * gain * idt(V(pulse_in), 0);
end
endmodule