Depending on how old school steel your singlespeed is, you could spread the rear apart (oo err missus) to become 148. I have sprung a 120mm road frame apart to 130 in order to fit modern gears, 135 – 148 is only a few mm more. But once I did it, I had to bend the dropouts a bit to get them parallel again, otherwise the rear wheel wouldn’t bolt in straight. A bit of a faff tbh. Then you could fit one of them skewer boost hubs scotroutes mentioned (which I hadn’t heard of before).
Depending on the dimensions, it is possible that hub adapters designed for QRing standard width hubs would have the correct spacing for boost width? And anyhow, if you are bending your frame to fit, a mm or so won’t matter.
Why do you want to do this?