HP 48GX - Center Text in the Display Area

[MNH]

How would I center text in the display area?

\<< DUP SIZE NEG 22 +
2 / \-> f \<< " " 1 f
START " " + NEXT
SWAP + \>>
\>>

1: "text string"

The above example string contains 11 characters. That means I'm left with 5.5 spaces proceeding and preceding the string if it were centered in the display area. My code fails because I can't use half of a space. What can I do?