Do you mean, for instance if you have your x's in A1:A6 and y's in B1:B6, and instead of having:
=LINEST(A1:A6,B1:B6,TRUE,FALSE)
You can do this, where values in A1:A6 are in the first set enclosed by {}, and values in B1:B6 are in the second set. You'll get the same answer:
=LINEST({1,0,1,1,1,0},{0.35,0.1,0.6,0.55,0.53,0.51},TRUE,FALSE)
Remember to still confirm with Ctrl Shift Enter