Set 1 row in an assignment block to read-only

Hello Experts,

I have the following requirement for an Assignment Block :

-------------------------------------
A       AA
B       BB
C      CC
D      DD
E      EE
-----------------------------------
T1    T2
-----------------------------------

Here the last rows indicate sum of the column values and it need to be read-only field but it should be sets with the column sum.

Any suggestions as to how to achieve this requirement?

Regards

Nisha