The script below handles your first issue
Names Default To Here( 1 );
dt = Open( "$SAMPLE_DATA\Big Class.jmp" );
colnames = dt << get column names( numeric,string );
meanlist = {};
For( i = 1, i <= N Items( colnames ), i++,
meanlist[i] = Col Mean( column(dt,colnames[i]) )
);
For the second issue, you could meet what you need by creating a character column and then create your 2 or more calculations, convert each of them into a character string, and then concatinate the values together, to place them into a List, convert the list to a string: Char(MyList)......which would end up looking like "{45, 34}";
Or lastly, you could save the list as an expression.
But as far as JMP automatically handling the results in analyses, it currently does not have that capability
Jim