The best way to do this is probably to use %CELL to refer to the other cells, and use + (the MDX concatenation operator). Here is an example that works in the SAMPLES namespace:
WITH MEMBER [Test].[Test] AS '%CELL(-2,0)+", "+%CELL(-1,0)' SELECT NON EMPTY {[HomeD].[H1].[City].CurrentMember.Properties("Population"),[HomeD].[H1].[City].CurrentMember.Properties("Principal Export"),[TEST].[Test]} ON 0,NON EMPTY [HomeD].[H1].[City].Members ON 1 FROM [Patients]
Output (as seen in MDX shell):
Population Principal Export Test
1 Cedar Falls 90,000 iron 90000, iron
2 Centerville 49,000 video games 49000, video games
3 Cypress 3,000 gravel 3000, gravel
4 Elm Heights 33,194 lettuce 33194, lettuce
5 Juniper 10,333 wheat 10333, wheat
6 Magnolia 4,503 bundt cake 4503, bundt cake
7 Pine 15,060 spaghetti 15060, spaghetti
8 Redwood 29,192 peaches 29192, peaches
9 Spruce 5,900 mud 5900, mud