Paul Furman wrote:

....

I don't have or know how to use external flash though I
could try reflecting the onboard flash with a white card
at the ceiling.

....

Any other suggestions? Should I back out & tell them to
hire someone else with flash because this is a hopeless
assignment? I enjoy low light shooting but this will be
really rough.

I think there are two options, obtain an external flash
or backout of it.

I shoot parties and many many random bits of life in one
local restaurant (located literally across the road, and
I use it as my living room), and have often done parties
at another.

A lot depends on the particular restaurant. How evenly
lit it is, how large the room is, how high the ceiling
is, and what color the walls and ceiling are.

But invariably it comes down to how to set up a flash,
because there simply is no other way. (Restaurants are
probably the only place where I routinely use flash as a
main light.)

Certain tables might have enough light, or might have
light at certain times of the day and not at other
times. That is useful for my purposes, but probably not
for your assignment.

One trick I've used for parties is to set up three
different flash units, each with an optical trigger, in
the corners of the room at ceiling height. It basically
dowsed the entire room with light every time an on
camera flash was fired. That eliminated the typical
harshness of flash, and it also made it easy to sit in
one corner and use a zoom to pick out interesting
compositions.

Flash works best if the ceiling and walls are bright.
And I would not do multiple flash units if others will
be taking pictures...

Usually I use an external flash mounted on the camera,
pointed straight up and with a regular sheet of white
paper wrapped around it and held with a rubber band.
Two small cuts on the side and a slight bend at the mid
point to angle the top half, above the flash, at 20-30
degrees makes a good enough diffusor. Again, it helps
to have ceilings that are low and highly reflective.

I also power the flash with an external (Quantum)
battery pack, and use a tripod as much as possible.

--
Floyd L. Davidson http://www.apaflo.com/floyd_davidson
Ukpeagvik (Barrow, Alaska)