B757-200 FLT WAS DISPATCHED ON AN ATLANTIC; OVERWATER OP ON ALTERNATE RTE THAT REQUIRED HIGHER FUEL RESERVES FOR THE RTE FLOWN AND FOR THE ARR FORECAST IN SJU.

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I WAS INFORMED BY THE RELIEVING DISPATCHER A FEW DAYS AFTER FLT LANDED; THAT HE HAD FILED AN ASAP RPT ON FLT XXX IN APRIL; ORD-SJU. I WAS WORKING THE CARIBBEAN DESKS THAT NIGHT AND WAS CONCERNED WITH TSTMS ALONG THE CAROLINA COAST; AS WELL AS FLORIDA. I SET UP A FLT ORD-SJU ON A COMPANY RTE WHICH TAKES THE FLT OVER SIE.B24.CHAMP/A300. THIS WAS TO AVOID THE POSSIBILITY OF ENRTE TSTMS. SINCE ORD-SJU FLTS ARE USUALLY PLANNED AS B43 (OPS SPEC) SPECIAL RESERVE RELEASES; THIS FLT INADVERTENTLY WAS FILED OVER A RTE WHICH HAS ENRTE POINTS FURTHER THAN CAN BE RELIABLY FIXED EACH HR USING CLASS 1 NAV FACILITIES. THIS FLT; THEREFORE; REQUIRED INTL ENRTE FUEL RESERVES; IE; E/RSV. SINCE I HAD FINISHED MY SHIFT; AND THE FLT DEPARTED LATER; I WAS NOT ABLE TO CORRECT THE ATC FILING. THIS FLT LANDED SJU WITHOUT INCIDENT; AND DID NOT POSE A SAFETY RISK DUE TO FUEL ON BOARD WAS SUFFICIENT FOR RELIEVING DISPATCHER TO CHANGE FROM A B43 RELEASE TO E/RSV RELEASE OR REMOVE THE ALTERNATE FOR SJU WHICH WAS STX. SJU WX WAS NOT CALLING FOR AN ALTERNATE NOR NEEDED ENRTE; BUT WAS ADDED AS A PRUDENT MEASURE FOR POSSIBILITY OF SHOWERS AROUND SJU AT TIME OF DISPATCH. SOME STEPS SHOULD HAVE BEEN TAKEN BY RELIEVING DISPATCHER TO AMEND RELEASE AND/OR CHANGE ATC ROUTING WITH AGREEMENT FROM CAPT WHILE THE FLT WAS ENRTE AND THUS FIND A WORKABLE SOLUTION ADHERING TO COMPANY AS WELL AS FAR REGS. SOME WAYS TO AVOID ANY POSSIBLE FUTURE INADVERTENT FILINGS ARE: 1) HAVING RTE MAP IN FLT MANUAL AND DISPATCH WORK DESKS WITH AREA COVERAGE WHERE B43 CAN/CAN'T BE APPLIED. 2) NAV DATA DEPT BLOCKAGE OF RTES UNABLE B43 FILING. 3) BETTER IDENTIFIABLE ENRTE POINTS FOR EACH COMPANY RTE MAKING B43 A VIABLE OPTION WHEN SITS AS THIS OCCUR; OR FLT GETS RPTED BY ATC.