At the moment I have the folowing:

|--------------+------+-----|
| activity     | Time | sub |
|--------------+------+-----|
| Activity A   |    3 |     |
| Activity B   |    5 |     |
| Activity C   |    2 |     |
| Activity D   |    7 |     |
| Activity E   |    8 |     |
| Activity F   |   12 |     |
|--------------+------+-----|
| Activity 1   |    9 |     |
| Activity 2   |    2 |     |
| Activity 3   |    4 |     |
| Activity 4   |    3 |     |
|--------------+------+-----|
| Activity I   |   23 |     |
| Activity II  |   51 |     |
| Activity III |   37 |     |
|--------------+------+-----|
|              |  163 |     |
|--------------+------+-----|
#+TBLFM: @>$2=vsum(@3..@-1)

But I want the following:
|--------------+------+-----|
| activity     | Time | sub |
|--------------+------+-----|
| Activity A   |    3 |     |
| Activity B   |    5 |     |
| Activity C   |    2 |     |
| Activity D   |    7 |     |
| Activity E   |    8 |     |
| Activity F   |   12 |  34 |
|--------------+------+-----|
| Activity 1   |    9 |     |
| Activity 2   |    2 |     |
| Activity 3   |    4 |     |
| Activity 4   |    3 |  18 |
|--------------+------+-----|
| Activity I   |   23 |     |
| Activity II  |   51 |     |
| Activity III |   37 | 111 |
|--------------+------+-----|
|              |  163 |     |
|--------------+------+-----|
#+TBLFM: @>$2=vsum(@3..@-1)

Subtotals from every range is calculated. Preferable from second to second last, so it goes OK when a range is added.

Is this possible?