Caddy is very overrated by the AFL community. He is not overly quick and not great by foot. He is not worth pick 13 in my book.
In saying that, a potential path we could take is to offer him a high dollar i.e. $750K one-year contract to come to us via the PSD (so high that it puts GWS and GCS off taking him) and agree to trade him to Essendon the year after for their first round pick. We need to spend the salary and we would gain a first round pick the year after. Caddy would pick up extra money and eventually get to Essendon and GCS would lose out on any compensation.
The other option would be to offer to trade down pick 13 to broker the deal a la Geelong and Mark Williams from Hawthorn to Essendon. (i.e. gain two picks in the early 20s).