This is why SW dont recommend saving up your syns, it makes it too easy to blow your limit on a boozy night out.
Shorts are the best method to have minimum syns for maximum drinks, but you could also make your syns last longer by alternating a pint with a diet coke/lemonade, or having a shandy with 1/2 a pint of lager topped with 1/2 pint diet lemonade.
For non-pub nights, there is a Czech beer which is quite a big sized bottle from Sainsburys, its low alcohol, but it's only 1 syn a bottle and I think the bottles are 500ml? So you can still feel like you are having a drink but without the high syns of beer.