Chainline is always solvable unless the chainring is going to hit the chainstay (a big problem when fixing an MTB frame) and I have worked out some very odd combinations.
You don't want spacers under the sprocket on a *fixed* hub. On a freewheel hub used as a fixed hub, it is OK - there is much more thread. Move the chainring in instead, by putting it on the inside of the spider, which usually reduces chainline by about 5mm*, or by using a shorter BB. Also look for a fixed sprocket that can be reversed to give a different chainline, like a Surly.
The target is to get within 1mm, and the only good way to measure chainline straightness is with a 600mm steel rule on the ring and sprocket, chain off (use the edge of the ruie, don't hold it flat against the ring as it will flex and give a misleading result).
*I understand this is deeply unfashionable in LFGSS circles but it is just as technically sound as putting it on the outside, especially if you are using a made-for-double crankset like most people
