You can create a new column that adds a grouping column that has different group values for each of the non Residual Gluecose value rows.

Here is the formula for the calculation of the group variable
As Constant( x = 0 );
If( Is Missing( :"Residual Glucose (g/L)"n ) == 0,
x
++);
If( Is Missing( :"Residual Glucose (g/L)"n ) == 1,
x
);
Then using Col Mean you can get the means you want

Here is the formula for the group mean calculation
If( Is Missing( :group ) == 0,
Col Mean( :"Temperature (Celsius)"n, :group )
)
Jim