Good morning (or whatever applies )

I am wondering if anyone can advise whether it is possible to do the following with Zen Cart ?
I have a situation where - rather than wanting to apply a discount for a particular customer - I would like to increase all of my sale prices for selected customers.
So - when the particular customer (s) log in - my prices are increased for that customer only.
I use quick updates add-on - & this has a facility to increase / decrease margin - but I can't restrict that to a particular customer...

Any thoughts on whether this can be done ?

Many Thanks !