Tabako (タバコ、たばこ、煙草) is another well-entrenched Portuguese loan, with particularly wacky kanji: they mean "smoke grass", which is reasonable enough, but you'd never guess the characters are read "tabako".
The other kind of ateji is when kanji are used like an alphabet eg 亜米利加 (A me ri ka). The second kind is mainly used for abbreviations in modern Japanese eg 米 is equivalent to writing "US" in English.
Forgive me if it seemed as though I was talking about usage ratios; I was merely saying that it's not uncommon to see them written in the kanji stylized form; in the case of konpeito, however, the kanji is by far the most common form (probably because the character semantics fit well). 天 also literally means tempura in a variety of derivative words.
But mostly I was just getting at how fundamentally integrated portuguese loanwords are in Japanese in general. shabon-dama (bubbles), kappa (raincoat), kabocha (pumpkin), and other's. Juban (a traditional undergarment) is probably the most surprising.