bash readline: Key binding that executes an external command

(Background: I'm a long-time tcsh user, gradually transitioning to bash, and trying to find equivalents for some useful tcsh-specific features.) In tcsh, I can define a key binding that executes an external command. For example, given: bindkey -c ^Gu uptime I can type "Control-G u" in tcsh, and it will execute the uptime command. I don't have to type Enter, the command doesn't appear in my history, and I can do it in the middle of an input line (I find the latter particularly useful for certain commands). bash has a similar key binding mechanism via the GNU readline library, with bindings specified in $HOME/.inputrc (or elsewhere). But after reading the info readline documentation, I don't see a way for a key binding to execute an external command. The closest thing I've figured out is to add something like this to my .inputrc file: "\C-gu": "uptime\n" but that doesn't execute the command; rather, it acts as if I had typed uptime followed by the Enter key. The command appears in my history (that's ok), and it works only on an empty line; if I type "echo control-Gu", then it prints uptime rather than executing the command. Another minor drawback is that the binding affects other commands that use GNU readline, such as the Perl debugger. Is there a way to simulate the effect of tcsh's bindkey -c in bash, by mapping a key sequence to the execution of a specified external command? If it matters, I'm using bash 4.2.24 on Ubuntu 12.04 beta 2.