Yes, that's possible. It's easiest to create new field for this in the script:
LOAD * INLINE [
Total Jan-June, January
Total Jan-June, February
Total Jan-June, June
Then use the new Period field instead of Month as dimension in your pivot table.
May be the solution of Gysbert is better than mine! But...
If you don't want to work on the scrip, I would suggest two chart-tables:
One first: a pivot table with Year and Month as dimensions and the expression =Sum(values). Feel free to mark "Show Partial Sums" to both dimensions (on Presentation tab) to see the totals. Example:
One second: a Straight Table with Year as the only dimension and the following expressions:
As you can see, I have used set analysis to set the intervals of months.
Hope it helps!