Draggable selection start and end points will come in OpenMPT 1.30. Pasting within the sample has also been available for a while now, but it's not really conventient: You either do it through the context menu, which means that you kind of estimate the paste position unless you zoom in a lot, or you use the shortcut and hopefully remember where you last clicked in the view (because that's where it will be inserted).

Hence I will hijack this feature request for clarifying how this feature could be improved: The cursor position (which is essentially the end of selection) needs to be visalized as a line. This should be supported by some convenience keyboard shortcuts (move cursor left/right [fine/coarse] and to start/end).