UPDATE: As of FogBugz 8.1, you can now collapse the wiki sidebar by clicking anywhere along its right edge:

This setting is remembered per-computer (via a broswer cookie), so you can collapse the sidebar on your netbook, but leave it open on your Jumbotron™ at work. :)
There are not currently any plans to implement this, but you can use the following bookmarklet
javascript:
var fVisible = !$("#wiki-page-search").is(":visible");
$("#wiki-page-search").toggle(fVisible);
$("#body").css({"margin-left": fVisible ? 270 : 0, "max-width": fVisible ? 960: "100%"});
When you're using the default template that comes with FogBugz 8, running that bookmarklet will toggle everything other than the body of the article off. (Running the bookmarklet again will turn everything back on)
For example, when used on http://developers.fogbugz.com:

becomes

You can also give this to everyone using this BugMonkey script:
$(function(){
var td = $("<td>").appendTo("#container table:first tr");
$("<a>")
.text("(toggle navigation)")
.attr("href", "javascript:void(0)")
.click(function(){
var fVisible = !$("#wiki-page-search").is(":visible");
$("#tbFull").toggle(fVisible); $("#wiki-page-search").toggle(fVisible);
$("#body").css({"margin-left": fVisible ? 270 : 0, "max-width": fVisible ? 960: "100%"});
})
.appendTo(td);
});