changing memory word with variable

Is there a way to choose with %MW you use depending on the value of %SW49? For example, i have 7 %MW:
-%MW4 that needs to be active when %SW49 :=1
-%MW8 that needs to be active when %SW49 :=2
-%MW12 that needs to be active when %SW49 :=3
-%MW16 that needs to be active when %SW49 :=4
-%MW20 that needs to be active when %SW49 :=5
-%MW24 that needs to be active when %SW49 :=6
-%MW28 that needs to be active when %SW49 :=7

so is there a way to say %MW0 := %MW(4*%SW49) on a operation block?