Some systems also have busybox installed in which case you may run:

busybox chmod +x /bin/chmod

Since you were asking for hacks, I just thought of another one:

mv /bin/chmod /bin/chmod.orig cp -a /bin/chown /bin/chmod

Now you have a /bin/chmod that's executable but it's actually chown (i.e. some other binary). Now all we have to do is overwrite it with the original binary.

dd if=/bin/chmod.orig of=/bin/chmod

It keeps the +x flag so you just stole the +x of another file for this one.

Of course, if all those alternative binaries (including the loader, perl, python, gcc et cetera) were chmod -x, fixing it from a rescue system may be the only option.