Like this. Since it has no kanji it has to be a reading, and to make it stand alone, i.e. not be tied to a kanji form, we tag it "nokanji".

@@ -13,0 +13,4 @@
+<r_ele>
+<reb>ヤジる</reb>
+<re_nokanji/>
+</r_ele>

I've run across this a couple times as ヤジる, and a google search turned up more occurrences of the mixed katakana/hiragana form, so I thought it might be worth adding it to the entry, but I'm not sure how to best include it.