Unfortunately, there is not an option for Text Field Word Wrap in the current Zebra Designer Software as of 2012-12-17 date.  If you want to achieve this you must also add ZPL code into the PRN file as per the instructions taken from the ZPL Programming Manual Below.

Sample PRN File With and Without Code

Code containing Word Wrap [highlighted in red]

Code Without Word Wrap

ZPL Programming Manual Excerpt

Here is also an excerpt from the programming manual about the ^FB command
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^FB   - Field Block
Description The ^FB command allows you to print text into a defined block type format.
This command formats an ^FD or ^SN string into a block of text using the origin, font, and
rotation specified for the text string. The ^FB command also contains an automatic word-wrap function.

Format ^FBa,b,c,d,e
This table identifies the parameters for this format:
Parameters
a = width of text block line (in dots)
Accepted Values: 0 to the width of the label
Default Value: 0
If the value is less than font width or not specified, text does not print.

b = maximum number of lines in text block
Accepted Values: 1 to 9999
Default Value: 1
Text exceeding the maximum number of lines overwrites the last line. Changing the font size automatically increases or decreases the size of the block.

c = add or delete space between lines (in dots)
Accepted Values: -9999 to 9999
Default Value: 0
Numbers are considered to be positive unless preceded by a minus sign. Positive values add space; negative values delete space.

d = text justification Accepted Values:
L = left
C = center
R = right
J = justified
Default Value: L
If J is used the last line is left-justified.

e = hanging indent (in dots) of the second and remaining lines
Accepted Values: 0 to 9999
Default Value: 0

Comments on the ^FB Command   
This scheme can be used to facilitate special functions:   
\& = carriage return/line feed   
\(*) = soft hyphen (word break with a dash)  
\\ = backslash (\)   
Item 1: ^CI13 must be selected to print a backslash (\).   
Item 2: If a soft hyphen escape sequence is placed near the end of a line, the hyphen is printed. If it is not placed near the end of the line, it is ignored.   
(*) = any alphanumeric character   

" If a word is too long to print on one line by itself (and no soft hyphen is specified), a hyphen is automatically placed in the word at the right edge of the block. The remainder of the word is on the next line. The position of the hyphen depends on word length, not a syllable boundary. Use a soft hyphen within a word to control where the hyphenation   
occurs.   
" Maximum data-string length is 3K, including control characters, carriage returns, and line feeds.   
" Normal carriage returns, line feeds, and word spaces at line breaks are discarded.   
" When using ^FT (Field Typeset), ^FTuses the baseline origin of the last possible line of text. Increasing the font size causes the text block to increase in size from bottom to top. This could cause a label to print past its top margin.   
" When using ^FO (Field Origin), increasing the font size causes the text block to increase in size from top to bottom.   
" ^FS terminates an ^FB command. Each block requires its own ^FB command.