These instructions apply to the desktop version of TOS (it's not clear if this approach would work with the web-based version).
Here's a way to draw TOS trendlines at the cursor position in the desktop version:
First, make sure you're in "pointer" mode so that the pointer arrow appears as your cursor. You may need to use the drawing menu at the bottom right of the chart to select the arrow. Note that this approach uses the context-sensitive right-click menu to draw just one trendline and then return to pointer mode, while using the menu at the bottom right keeps you in whatever drawing mode you've selected. An example of this action and the context menus is shown in the image, below.
Also, for precision, you may want to enable SNAP to OHLC, which will pull a nearby-placed point to the nearest bar extreme, as if a magnet was pulling the drawn object to the nearest bar part. That's set via the General tab in Chart Settings.
With the cursor showing an arrow pointer, position the cursor at the desired start point, RIGHT-click to get the context menu, and select the trendline option (at the upper-left of the popup drawing tools). The line will anchor where your cursor was when you clicked, and you'll then move the cursor to place the second anchor at the desired location with another left click.
Once positioned, you can move a trendline to a specific bar position by first left-clicking on the trendline to select it, then clicking either of its control points to adjust it. The control points are squares on the trendline, and if you click on one of the squares, you can move that part of the line to 'swivel' it with the other control point staying in place. This way, you can place your line close to wherever you'd like it to be, then use the control points to locate it to the desired position. Whether the line extends to the right or left is set via the trendline attributes, which can be adjusted by double-clicking on a placed trendline.
To move the whole line while preserving the angle, left-click on it anywhere except on the control points, and you can move the line at the original angle to wherever you'd like.