Horizontal Running Total with Table References

Hey all,

I'm writing a formula to calculate a horizontal running total in a table. To do so, I need to be able to lock the first column but unlock the second column so that as the formula is dragged across the columns the sum range will expand. This is easy to do without table formulas, like so:

Formula:

=SUM($A$1:A$1)

But I'm unsure what the syntax is for a table formula.

Unlocked:

Formula:

=SUM([Table1[Column1]:[Column2])

When it is dragged to the right:

Formula:

=SUM([Table1[Column2]:[Column3])

Locked:

Formula:

=SUM([Table1[[Column1]:[Column2]])

When it is dragged to the right:

Formula:

=SUM([Table1[Column1]:[Column2])

Ideally, I'd like Column1 to lock but Column2 to become Column3 when the formula is dragged to the right. Is this possible?