Pumping for occasional bottle feeding

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8 week old baby is breast fed. From time to time I would need DH or a relative to give a bottle of EBM if I have to be out (appointments, DC1 swimming lesson etc). I have pumped milk occasionally and have frozen this but will soon have exhausted this supply. I usually breastfeed baby before I head out so the bottle is in case baby wants milk while I'm out (2 hours max); she does feed frequently, so is likely to need the milk while I'm out.
Is it possible to have sufficient stash of EBM if i pump occasionally? It can take me a few days to get 2oz. The odd time I've been able to pump 80ml but this is rare. Over the last two days I've only expressed 10ml only! I don't love expressing and it's hard when I am feeding all the time! I have 2 manual pumps already so don't particularly feel I want to get an electric one for only occasional use- a medela one and a Philips avent one.
Is it achievable to pump for occasional use?

Have you tried pumping from one boob whilst she's feeding from the other? I did that first thing in the morning with an electric pump and would get between 4 and 6oz in 15 minutes.

Thanks for replying. I tried that this morning, interestingly enough and managed 3oz. It was a job, however as I had to keep her on one breast in the crook of my arm while I used a manual pump on the other side! Also helped that DC1 had gone out with DH. Mon-fri this would be difficult as DC1 has to get ready for preschool. But pumping on weekends would probably be fine. The fact that baby doesn't like the bottle at all might limit the use of EBM anyway!