Instead of a line, draw it as triangle, with 3 collinear points. However, some lines will really look like triangles, because I remember MT4 rounds some of the point coordintes.
Use the OBJPROP_RAY property to turn off the trending. The following (entirely arbitrary) example draws a line from the low 10 bars ago to the high 5 bars ago.
string strObjectName = "Example line";
ObjectCreate(strObjectName, OBJ_TREND, 0, Time, Low, Time, High);
ObjectSet(strObjectName, OBJPROP_RAY, false);
If you are talking about drawing a tendline on the screen manually try this:
draw a trendline anywhere. double click on it, and 3 tiny boxes appear, right click and a dialogue box opens, select properties,then in the parameters tab uncheck the "RAY" box.
Don't resurrect nine year old threads without a very good reason.