Yes, I'm a firm believer in using washers on non-eyelet rims. Try to find decent ones in Stainless or Brass, and if the rim section is narrow at the seat, make yourself a small jig to curve them so they seat nicely into the rim.
Many years ago working with thin section alloy rims I used to use a bit of body filler under the washers to spread the load. While it was still soft, I'd build the wheel, and tighten it enough to bed the nipples and washers, Then I'd let the body filler cure before applying final tension. Using that technique I eliminated the splitting that those rims were famous for.
I still have and occasionally ride an old set of Italian built track wheels, wherein the builder used leather washers under each nipple. Those have taken tons of abuse as street wheels and are still in great shape, other than the effects of almost 50 years of weathering.
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