I want to feed a horizontal wire antenna (approximately 150' long at 50' or more above the ground) for multi-band HF operation with an off-center (25-33%) feedline. The element wire will have no support between the (well isolated) ends and the end supports aren't very rigid (large, old trees with twiggy canopies.) I want to avoid suspending any large mass (transformers, baluns, chokes or other heavy devices) from the horizontal wire or feedline; ideally just coaxial or ladder/open wire type feedline from the ground to the antenna. Expected TX power level is 500W or less.
Obviously some impedance matching solution is necessary for multi-band operation. Common-mode current on the feed line is inevitable for several reasons (imbalanced load, capacitive coupling between the elements and the feed line, etc.)
The question: is there any conceivable approach that can be applied strictly at ground level where I am free to employ any device or technique that will a.) provide necessary impedance matching for multi-band operation b.) either eliminate common-mode current or obviate the impact of common-mode current (feedline radiation, pattern distortion, etc.) on the feedline and c.) keep the feedline losses low?
I believe the answer is no, but I'd like to know if I'm overlooking anything. I am (painfully) aware of myriad other antenna arrangements that can avoid some or all of the issues with the above antenna; please confine the discussion to the configuration described above. And thank you.