A investor could get hold of a significant number of...

A investor could get hold of a significant number of convertibles in several ways.
1) Being a significant holder & taking up their full entitlement
2) Being a large holder & buying more than their entitlement
3) Participating in any post offer sale of notes not taken up by existing holders
4) Buy notes off market from other holders.
So yes although the market in the notes will most likely be very illiquid it is possible for someone get sufficient notes to make it worthwhile shorting the share.
It will be easy to see if this happens as there are currently zero short positions on CSS.

Re the opportunity
I took part in unlisted investment opportunity last year & the company offered me extremely attractive offer to invest further. Definitely not a P&D scheme.