How many people are you hoping to upgrade? Upgrade availability ex UK is generally quite limited in advance due to the popularity of the routes.
December is a quieter month for business travel so that may help increasing
the chances. Manchester has the 380 which means more seats. However, the week before Christmas, for example, is a busy travel time and DXB is a popular destination at Christmas. I seem to recall reading somewhere it was in the top 3 holiday destinations last Christmas for UK travellers.
If you have any ideas of dates let me know and I can check upgrade availability on expertflyer for you.
Also buying Flex tickets will mean you need less miles to upgrade.