If you really were to do this, despite all the overwhelmingly good reasons not to, as in a pure mental exercise or an economic situation where there's lot of brainpower plus computers and internet connectivity, but extreme physical scarcity of new rims but you can somehow get spokes in all sorts of lengths, there are basically two paths:
- Use real math skills to model the whole thing out on paper. Congrats to anyone who can do that.
- Use any 3d CAD software to create a simple model of the rim and hub. It just has to be a bunch of circles with points spaced evenly along. For example, the rim is two circles, one for each side's offset, with 16 points on each and with one set originating a distance away from the first equal to 1/32 of the ERD/circumference (the ERD is the circumference of both circles). Then put in the valve hole as another point.
Same deal with the hub, two circles for the flanges spaced apart from each other per the hub geometry, with points offset. Set up the drawing so the hub is in the correct alignment with the rim in all the obvious parameters to make it be a dished wheel, so that the last thing you're figuring out is the rotational alignment of the hub with the rim.
Then, the way I think this would go for 1x, is on each side of the hub you're going to be deciding two holes to leave empty, 180 degrees away from each other on each side. Choose one flange and ignore the other. On the flange you're working with, align the hub rotationally so there's a straight line between the valve hole, the empty holes on that flange, and the wheel center. Lock the hub rotation there. Then draw in 16 lines between the other hub holes and that flange's offset side of the rim to create your 1x lacing pattern on that side. (You don't say which Spank rim you got and some of them have been set up for cross-lacing, another curveball in all this since if you do have one of those rims you'll be punished more for going with one of the lacing permutations that has you ignoring the directionality of the drilling).
For the other flange, you have the choice of making the unused holes be right next to the first set of unused holes on the other flange, or offsetting them away some number of holes. The latter is geometrically dirtier (it can't be exactly 90 degrees away because of the stagger) but I think it would probably avoid stress risers in the flanges better, so probably do that. Then draw in 16 lines for that side's 1x pattern.
The 32 lines are now your "pure geometry" spoke lengths. Then compensate for spoke elongation and rim compression as you would with any wheel, and buy those spoke lengths. I believe on paper it's going to be 16 different lengths, 8 per flange, but I don't know how close it will be after rounding to whole numbers.
Editor's notes: the other side would have different spoke lengths if the wheel is dished (which I'd imagine your rear wheel is). Regardless, the above image verifies Nathan's hypothesis that there are 8 different spoke lengths per flange. You can access my Autodesk Fusion 360 CAD file here and input your wheel's dimensions to get your exact spoke lengths. Here are the (arbitrary) parameters I used to model this specific wheel:
I would caution against any lacing pattern that mixes up the drilling offset direction of the rim. Hub motor wheels can struggle with spoke angle at the nipple at the best of times and basically have no tolerance for pushing it further.
