That depends on what exactly you mean. The ICS Input Box happens to be generated by XBoard's generic dialog generator, which also generates, for example, the Move List. So making the text field in there higher and making it autowrap is just a matter of setting a few flags in the table that specifies what should be in the dialog.
But I don't think it would be feasible to keep lines you have already sent to the ICS in there. Once you type enter, the text should be automatically sent, and the box cleared to accept the next command. So there never can be more than a single 'logical line' in the box, although because of auto-wrap it might be displayed as multiple lines. You can recall old lines in the box anyway by using the arrow keys.
Btw, if you feel adventurous, you might want to have a look to the version that does away with the console and also sends the output to the ICS input Box (which in other respects is very obsolete now). It can be found as the last snapshot in the 'chat' branch of my on-line repository:
http://hgm.nubati.net/cgi-bin/gitweb.cg ... heads/chat . I abandoned it at the point where I discovered it was impossible to colorize the text selectively in that window. It would have many advantages, though: XBoard could in principle size and position it, but also react on mouse-clicking in the window by selecting the word you click, and using it in the text-menu commands. (None of this implemented yet in that version, but I know how to do it.)