Yes, there is a workaround to calculate the geometric mean of an array of numbers that includes negative numbers in Excel. Here are the steps:

1. Use the ABS function to convert all negative numbers in the array to positive numbers. For example, if your array is in cells A1:A10, you can use the formula
   Code:

   =ABS(A1:A10)

   in another column to convert the negative numbers to positive numbers.
   
2. Use the GEOMEAN function to calculate the geometric mean of the absolute values of the numbers. For example, if your converted array is in cells B1:B10, you can use the formula
   Code:

   =GEOMEAN(B1:B10)

   to calculate the geometric mean.
   
3. Use the SIGN function to determine the sign of the original array. For example, if your original array is in cells A1:A10, you can use the formula
   Code:

   =SIGN(A1:A10)

   in another column to determine the sign of each number.
   
4. Use the PRODUCT function to multiply the geometric mean by the sign of the original array. For example, if your sign array is in cells C1:C10, you can use the formula
   Code:

   =PRODUCT(C1:C10)*GEOMEAN(B1:B10)

   to calculate the final geometric mean.

This workaround allows you to calculate the geometric mean of an array of numbers that includes negative numbers in Excel.