Tie logic values to vdd/gnd within Encounter

Hi,

I'm using Encounter for Place & Route of a synthesized verilog netlist.
The problem is that the synthesis tool (BuildGates) created assignments 
such as:

module m(dout);
  ouput [0:15] dout;

  assign dout[15] = 1'b0;		// <--- problem

(...)

But Encounter doesn't connect the net dout[15] which has the fixed value 
1'b0 to the vdd net, although I used the following commands within
Encouter:

  globalNetConnect vdd -type tiehi -module {}
  globalNetConnect gnd -type tielo -module {}

I already tryed to insert tiehi/tielo cells, but I cann't find any 
tiehi/tielo cells within my synthesis libraries.

How can I tell Encounter to connect 1'b0 to gnd and 1'b1 to vdd?

Thanks,

Andreas