@rant How are you calling the URL once you get it via nlapiResolveURL? If you are concerned with hitting the URL length limit, you can use nlapiRequestURL and post your stringified JSON. Something like

nlapiRequestURL(<your url>, JSON.stringify(data), null, null, POST)

if its client side or

nlapiRequestURL(<your url>, JSON.stringify(data), null POST)

if server side.