hi gaynor
sounds like a great idea to get you a bit more sleep. I don't suggest you do it though! Don't know where you are from, but in the uk we are advised not to wean till 6 months(most people seem to start ealier though) so a rusk isn't suitable for a baby as young as yours.
don't feel daft for posting this question, when I've been sleep deprived I've come up with all sorts of crazy solutions, inculding velcroing dd's sleeping bag to the matress so she can't roll over :oops: don't worry I didn't actually do that!
sounds like you may be desparate for extra sleep, if you're not bf could someone else do a night feed for you? have you tried cluster feeding? I fed dd at 4pm, 6pm and 7pm when she was that young, it helped a bit.