After the user drops a Guide on the artboard they can 'click' the Guide Selector UI which will auto-place another guide using the same pixel measurements as the previous dropped guide.

e.g. User drops a guide at 50 pixels from the Top they then click on the Guide Selector UI element, not drag, and another guide will be automatically placed at 100 pixels from the top (+50 pixels from the previous guide).

Clicking twice on the Guide Selector UI twice in a row would auto-place 2 more guides; first at 100px and second at 150px; thereby creating a 3 guide set up quickly.