We have the same issues. My kids are young (my CFer is 2) so I use snacks to add calories to Ben's diet but keeping ours the same. Smoothies are a good way to fill in the cracks and a CFer could do this a couple times a day or at meal times to add calories and still eat the same meal that is prepared for all. You can add extra protein from Rice Powder or Jay Robb's Egg Protein (our favorite at the moment) after pouring off the non-cf version into glasses.
Another way to add calories to your meals is to create things which can have, like you said, a topping. For example, take some chicken tenderloins, dip in flour, egg then Panko (Japenese) bread crumbs, fry in coconut oil(this stuff is great tasting!), set a side (you can make more than you need here too for lunches and snacks). Then make a fresh fruit salsa with mango, cilantro, black beans (protein), sea salt, lime and olive oil. Make a frozen packet of rice up in the micro with a little cilantro and lime sqeezed on top. Then prepare a little coconut milk side with coconut milk, a bit of oil and toasted coconut. Assemply non-cf version with rice, chicken and salsa and then just add the coconut concoction on top of the CF version. Serve with tropical smoothie for even more calories for the CFer...water for everyone else. This takes all of 1/2 hour to make!
Use Sunday's as prep day and boil a couple chicken breasts, hard boil some eggs and make some great chicken or egg salad for snacks and lunches. Separtate out the CF version and add a bit more calories with a little extra mayo or omega 3's with walnut oil (especially good in chicken salad) or even MCT.
My favorite chicken salad is cubed chicken (organic if possible), red grapes, mayo, walnuts (adds protein and omega 3), sea salt, and a but of tarragon if you like it. You could also add ground flax seeds for even more good fat and fiber. This gets you 2-3 days work of snacking and lunches (pita pockets, wraps, on a salad).
Egg salad is easy and adds alot of protein throughout the day if you like it. Eggs chopped, pickle, mayo, sea salt, and a bit of red onion. This is good on cracker at snack times and of course.
You can also grill up some flank steak and add this to salads and wraps for the week.
Hope this helps. There will be more stuff like this on my site below...just waiting for the chef to send me the files to put it up.