I think I have it figured out in a round-about way...

I will post my method in case it helps someone in the future (or if I made a mistake or there is a better way, someone can point it out). The pictures below show a "test" footprint with the steps I used.  Result shown below (LED2) using the "Photo View" in a sample circuit. 

Pads will always default to being exposed. There are at least 5 ways to do this. 1, 2 or 3 are "correct" ways to do it. $ and 5 are quick and dirty and may well come back to bite you. 1. 1. Make a PCB Footprint as in the right hand picture; 2. Edit the Solder Mask attribute to use a negative value so you can close the solder mask off (make it at least half the smallest dimension of the whole pad then make it negative); 3. Add 4 more top layer pads to the dimensions and positions of the left hand picture and give them the same numbers as the big pads they are going onto. 2. 1. Make a PCB Footprint as in the right hand picture; 2. Edit the Solder Mask attribute to use a negative value so you can close the solder mask off (make it at least half the smallest dimension of the whole pad then make it negative); 3. Add 4 Apertures in the Solder Mask Layer to the dimensions and positions of the left hand picture. 3\. \(I did make this work once but not sure I remember all the steps\.\.\.\) 1. Make a PCB Footprint as in the right hand picture; 2. Convert the pads to polygons; 3. Edit the polygons so that their centres are the centre points of the exposed areas; 4. Edit the Solder Mask attribute to use a negative value so you can close the solder mask off except for the exposed area of the pads. 4. 1. Make or find a PCB Footprint as in the let hand picture; 2. Route tracks to it on the PCB; 3. For each of the extended pad areas, add a Copper Area (set to solid not spokes) assigned to the relevant net name. 5. 1. Same as 1 but use a Solid Region set to Solid.

@hafridi21, Well done and thanks for posting your method! Our posts must have gone up at about the same time. :)

Thanks for replying @**andyfierman.** Looks like the first method you suggested corresponds to what I did, so I'm glad it's considered to be a "correct" one. Also, thanks for your contributions in this forum. You've posted a lot of info on other threads that I've found very useful.

Thank you. :)