Loading multiple grids from json with multiple roots

Is it possible to use a ListLoader and JSONReader to populate multiple grids from a multi-root json object? I'm attempting to load 3 grids -one for machines, one for mab and one for users - from the following JSON:

{
"machines" : [
{
"total" : "1",
"user" : "dtc2100cc1bbd6e",
"mac" : "00-21-cc-6d-b1-eb"
},
{
"total" : "1",
"user" : "dtc26009b242e86",
"mac" : "00-26-B9-8E-42-62"
}
],
"mabs" : [
{
"total" : "1",
"user" : "dtc2100cc1bbd6e",
"mac" : "00-21-cc-6d-b1-eb"
},
{
"total" : "1",
"user" : "dtc26009b242e86",
"mac" : "00-26-B9-8E-42-62"
}
],
"users" : [
{
"total" : "1",
"user" : "dtc2100cc1bbd6e",
"mac" : "00-21-cc-6d-b1-eb"
},
{
"total" : "1",
"user" : "dtc26009b242e86",
"mac" : "00-26-B9-8E-42-62"
}
]
}

I can easily extend JSONReader for each of the 3 roots, creating a MACJsonReader, MABJsonReader and UsersJsonReader but the ListLoader only accepts one reader.