Is it possible to activate any cell by doubleclicking it,
for the purpose of drawing a diagonal line in the next
cell higher and to the left, and continue upwards diagonally
until a margin is hit (such as column A, or horizonally row A.. Z...

A B C D E F
1 \
2 \
3 \
4 \
5 123

Similarly, ascending to the right

A B C D E F G
1 /
2 /
3 /
4 /
5 123

From any cell

With Thanks