This is not generally done by pinging or ARP trickery. It's done by paperwork.
Every request for IPv4 address assignments requires detailed justification, showing that existing addresses are fully utilized and that (in the case of ARIN) the new assignment will be 80% utilized within 30 days. See the ARIN Number Resource Policy Manual for complete details. RIPE and APNIC have similar policies.
The justification typically consists of a report stating what all of the existing IP addresses are currently used for, and how (and if applicable, for whom) the new IP addresses will be used.
The rules have been significantly tightened up in the last couple of years, now that IPv4 /8 blocks are exhausted.
On the other hand, you can give out IPv6 like free candy, and you should do so. Give everyone enough IPv6 subnets to last them for decades, and strongly encourage them to use their IPv6 allocations.