Nope. Illustrator (you know...this ostensibly "professional" drawing program) doesn't provide even rudimentary "dumb" dimension tools (just as the program still dosen't even provide live geometric shape primitives like any other drawing program under the sun does).
Cheezy workarounds can be (and have been) devised with scripts to create dumb dimension labels, but updating when objects change really requires special dimension objects. Scripts loose their object-specific references when the script completes, or when the script's palette is closed, unless you code into the script some kind of object labeling, which would become cumbersome real quick.
If it's a frequent need, you need a proper feature for this, and you're just using the wrong program. Use Draw or Canvas. You can probably buy a competitive side-grade to either of those programs for not much more than you pay for an elaborate plug-in, and get alot more value in the deal.
CADtools does provide this option. In CADtools 2-7, make sure that "Live Dimensions" is turned on in the CADdocument panel. Then, after stretching the rectangle, simply cick the "Update Links" button the CADstyles panel. If you have CADtools 8, then you just need to have "Attached Dimensions" checked in the CADtools preferences and the udpate will be instantaneous as soon as you stretch the rectangle.
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