How to make dimers or trimers by PCR?

[Tony Day]

I am using PCR to make linear copies of a plasmid for mutagenesis.  I
would like to be able to make linear (head to tail) dimers or trimers, but
can't think of a way to do it (Ligation strongly favours
recircularisation).  I don't want to make long multimers as this has
already been shown to introduce additional mutations.

Any ideas gratefully received.

Thanks

Tony