There isn't at the moment, unless you can find some SIP destination (perhaps among the SIP Broker peers) to which you could forward the call that would answer 486 BUSY to every call.
Actually, I've been thinking that a SIP server (VoXaLot or other) that just dishes out canned responses could be useful. For example, some dummy SIP URIs could be set up, such as:
reply486BUSY@voxalot.com (responds with 486 BUSY to every call).
reply380PSTN@voxalot.com (responds with 380 Alternative Service, PSTN)
(useful for people using Japanese ATAs)
Some SIP devices have a "blacklist" - a list of phone numbers from which calls will be refused. You might be able to use that feature in your phone or ATA to avoid being interrupted by SIP probes.