Set a propane torch where its comfortable and at the correct angle and warm the pin with it. A hot plate works well to warm everything and may get it where you need to be.
otherwise its cast hard and fast, dipping the corner of the mould into the molten lead may also transfer enough heat to the pin the problem is the part of the pin that does the work isn't going to be in contact with the blocks but in open air meaning heat has to transfer thru the pins mass itself.
As said above when casting cast don't sort or cull.,cast and at a brisk pace.