I've never tried this, so you really some suggestions from others (like MaxQue above), but you could overlap your butt and ribs if you have room in your smoker. Babybacks will only take about 3 to 4 hours. I usually cook butts at 250 and ribs at 225, so I'd just reduce the cooking temperature to 225 when I put the ribs in. Although 250 would probably be fine for the ribs too.
I don't know what kind of meat will hold the best, but I'd FTC (foil/towel/cooler) the butt rather than put it in the oven. It won't dry out that way. In a small preheated ice chest with plenty of extra insulation thrown in, it should hold for 4 or 5 hours.
If you go the oven route, double wrap the butt in foil, put it on a pan to catch any leaks, and set your oven on the lowest temp it will go. On most modern ovens that'll be around 170.
I don't know about tri-tip.