Most one arm exercises can be self assisted. Try these and see if you can elogate the bicep without straining your forearms. But remember if you have weak forearms and wrists you're at a higher risk for elbow tendonitis and those epicondyle tendons heal very slowely.

1 arm preacher (like Papapump said)
Concentration curls (both supinated and hammer style)
1 arm cable hammer curl.

Focus on form and a good squeeze at the top of each movement. Pause and stretch at the bottom as well.