There is a workaround, but it reformats the cell to text so you'll have to create a hidden column with the numbers with a decimal point for your calculations. Also, all numbers must be rounded to 2 places.

If your number is in cell A3, for example:

=CONCATENATE("€ ", LEFT(TEXT(A3,"# ##0.00"),LEN(TEXT(A3,"# ##0.00"))-3), ",",RIGHT(TEXT(A3,"0.00"),2))

This will give you a comma for a decimal and a space for the thousands separator.

You may need to add the format "# ##0.00" to the custom formats for cells.