Ho can i add caption to the column names and nor showing up all the coulmns by default for the end user.

Hi Team,
Currently, I get 'data' to be shown on flexmonster grid as a json response, as below:

1. ColumnA: "2015-01-01T00:00:00Z"
2. ColumnB: "XYZ"
3. ColumnC: "1234"
4. ColumnD: "AB"

I have the 'slice' as below:
{
"rows": [
{ "uniqueName": "ColumnA", "caption":"Column A" },
{ "uniqueName": "ColumnB","caption":"Column B" }
],
"expands": { "expandAll": true }
}
Now in the grid, I am able to view data for the 2 columns. 'Column A' and 'Column B' (with spaces)are shown up on the grid by default and 'ColumnC' and 'ColumnD' are unchecked column fields in the grid, and the user has to manually include these two columns to view all 4 columns.
 
Issue 1- How can I have caption for all the JSON keys in the data.
     Any solution other than, having to include all the columns in the slice 'rows:[]' object for all the individual reports. As I do have a number of reports with varying numbers of columns returned in the json data.
Is there any way I can have a common .json file, with a list of all the columns(as keys) and corresponding caption(as value) and show values form this json file as the column names for the grid data.
 
Issue 2- Including the columns in the rows:[] object.
     All the columns in the rows[] are displayed in the grid by default. How do I selectively show up the columns in the grid?
In the above example, I get to see Column A and Column B in the grid by default. I want only column A to be displayed and then check/uncheck the other columns from the fields toolbar menu.
 
Thanks in advance!!!