If it doesn't come naturally I wouldn't force it as you are likely to end up rather red faced. Plus he may not appreciate that kind of sense of humour, everybody is different and funny or quirky in their own little way.
I really wouldn't try to be something I am not.
Just picture worst case scenario; you make a funny, he laughs and asked you out on a date yadda yadda yadda, years down the line you marry, etc etc. and at the altar it suddenly dawns on him that you are not really the witty girl he fell in love with at the photocopier.
Anyhoo, I liked you're dry response to Neil - everyone is sparky in their own different way :-)