YOU SAID:

i really can't come up with one.

INTO JAPANESE

私本当にことはできませんを思い付きます。

BACK INTO ENGLISH

I can not think of what I can not do.

INTO JAPANESE

私ができないことは考えられません。

BACK INTO ENGLISH

I can not think of something I can not do.

INTO JAPANESE

私はできない何かを考えることができません。

BACK INTO ENGLISH

I can not think of something I can not do.