It's hard to do an orbital plane change, and damned hard to essentially go from the plane of the ecliptic to a solar "polar" orbit. Ulysses used a Jupiter gravity assist to do the plane change.

It's not easy to drop close enough to the Sun to do a substancial gravity assist maneuver. A Jupiter flyby could do the trick. You'd fly out to Jupiter and use the gravity assist to go essentially retrograde towards the Sun. I think if you aimed at the leading edge of Jupiter at a fairly high altitude and used the gravity assist to impart a lot of delta-v against the normal rotation of the planets around the Sun. The goal would be to fly substancially within Mercury's orbit. You'd need some damned good heat shielding/reflectors to protect your vehicle but it could be done.