Tomek,
try to use an extra sheet. In there use =Sheet1!A1 and copy for three
rows and two columns. Immediately down use =Sheet1!A100 and repeat.
Then use your XIRR(). Back in Sheet1 use ='Helper Sheet'!cell number
with XIRR().

Change the names of the sheets as necessary, enclosing sheet name in
single quotes if it contains space.

HTH
Kostis Vezerides