its a missing feature.
$ does not work because the IDE translates it to 0x so gdb takes it as hex.
You can compile the ide with DBG_WITH_DEBUGGER_DEBUG defined. That gives you a direct interface to gdb in the "debug output" window.
This is not an official feature, it works as is, and thats all.
Note, you must not (are not allowed to) issue run/step commands this way. doing so IDE and gdb will loose sync.
But you can modify data.