If you the sequence of mismatch is known, I would recommend amplification with one of primers specific to the mutated and normal sites. Additionaly primer specific to mismatch will not amplify the normal cDNA.

Amplify across the mutated splice site in the cdna to a reverse primer that should exist in the normal and the mutated cdna. The length of the amplicon should tell you if alternative splicing has occurred and its sequence will tell you exactly how the sequence has been changed

 You can directly sequence the cDNA, designing primers from the upstream and downstream primers from the exons adjacent to the splice site mutations would help.

Best