Is it permissible to conclude a sale before receiving possession when exchanging two items subject to usury, but where the underlying causes (illah) of the usury prohibition differ between them?

Primary text

If the causes of usury differ, such as exchanging a measured commodity (makil) for a weighed commodity (mawzun) according to those who apply both causes, then separation before possession is permitted. This is the position of Abu al-Khattab and Al-Shafi'i. The justification is that since their respective causes are different, separation before possession is permissible, analogous to the exchange of a price for the priced item (thaman bi-l-mithman).