Bumble bees nesting in wall of lean-to greenhouse

Hi,
I have just bought the materials for a small lean-to greenhouse which I am constructing in an old outside toilet. Now I am putting the door on, I have noticed a small hole in the wall which seems to be the point of entry/exit to a bumble bee nest (red-tailed variety by the look of it).
Is there any way I can get the bees to leave the nest before sealing the hole? I don't mind the idea of the bees being there, but I figure that once the greenhouse is 'sealed' (even though there will be a space for the bees to get out, it might be dangerous if the bees got angry at not being able to enter and exit as normal...
Any ideas anyone???