How can I enable customer pick up from a non-default location in checkout?

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Im struggling to allow customer pick up from checkout from a location different to my default shipping address.
It seems I have to have inventory in both places to allow me to do this, but on my previous site I was able to have 1 quantity and allow the customer to collect and bypass shipping. whereas now I need to have at least 2 products to be able to do this as it requires inventory in both locations to allow pick up on checkout. This is not possible when some items are one off pieces. Is there any way around this?
Thanks Kate