For a attempted biceps stretch, rather than any ( however slight) bicep contraction, consider extra wide grip DL's. With a regular grip (over hand) or even a curl grip. Trying for a bicep contraction with a full stretch, than the wide grip BB curl. Full hanging chins, either two or one arm. Rope climbing (a very rare exercises today) from a full overhead reach gives a great stretch. Not only the biceps but the lat's also.
If anyone has done serious construction work with a wheel barrel they know the affects the day after. Reason why Farmer Walks are included in any bicep stretching action. Can do Olympic snatches & cleans also.
Drag curls (suggested as a Gironda invention?) keeps tension focus through the full movement. But not really a biceps stretching function. As Chaos mentioned, Preacher/Scott curls, but probably better with a DB one arm at a time. The top of the preacher bench should be pretty well jammed into the side/arm pit of the person doing it. All giving better focus on the bicep stretch. Curl grip BB rows (Dyslexic's offering) are good with a close to extra wider grip. If fact, that exercise is one of the better lat builders for a lot of guy's.
Doing regular BB curls, with a close grip (almost touching the hands) and the elbows jammed into the waist/abs also allows a good stretch. And a outstanding bicep contraction/cramp at the top of the movement. Good Luck.
