We have just been going through this ourselves, I had a first aid course on Tuesday and DD2 (almost 9 months) was going to come with me, but as she is sick with RSV it wasn't an option.

So we took a gamble and DH stayed at home with her and we had a sipper bottle which has a teat that looks like a straw, but she can bite/suck chew on it to get milk out. I was gone for 9 hours and she had a BF before I left and as soon as I got home, but over the day she drank about 180mls from the bottle, it short small bursts (50ml or so at a time). So it was enough to sustain her during the day and she filled up when I got home. We also had Neurofen syringes ready as we know she will take gaviscon from those, so we thought worse case DH can syringe it into her, but in the end he didn't need to. But it had to be DH do it any other time I have offered it she has lost the plot, because of course the boob is right there.

DD2 isn't eating solids atm as she can't cope with them and being sick, so we were heavily relying on her taking something from the cup. I think it works better if you aren't there as they know they should be having the boob