A GROB 115 TOOK THE RWY FOR TKOF AT CXO IN FRONT OF A C340 ARRIVING ON AN IFR FLT PLAN.

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I WAS OPERATING A GROB 115 AS A CFI PREPARING FOR TKOF. THE STUDENT PLT WHO WAS IN CTL OF THE ACFT WAS WAITING BEHIND 2 OTHER ACFT AT THE END OF RWY 14 (CXO) AFTER THOSE ACFT DEPARTED THE STUDENT CLRED THE AREA FOR TFC. THERE WAS A LITTLE CONCERN DUE TO A SCATTERED AREA OF CLOUDS AT APPROX 1200-1500 FT AGL ALONG THE EXTENDED CTRLINE OF RWY 14. THE STUDENT COMPLETED THE ADVISORY CALL ON THE CTAF PRIOR TO XING THE HOLD SHORT LINE AND THEN PROCEEDED TO LINE UP ON THE CTRLINE. THE STUDENT MADE 1 MORE CALL ON THE CTAF STATING HE WAS GOING TO HESITATE IN POS MOMENTARILY FOR A SIMULATED SHORT FIELD TKOF. THE NEXT XMISSION ON THE CTAF WAS 'GROB; IF YOU HEAR THIS XMISSION; YOU BETTER CLR THE RWY; THERE IS A TWIN CESSNA ON FINAL I AM ON AN IFR FLT PLAN.' THE STUDENT REJECTED THE PLANNED TKOF AND CLRED THE RWY AT THE CLOSEST INTXN TURNING R ONTO RWY 19 AND ADVISING ON THE CTAF THAT THE GROB WAS CLR OF RWY 14. DURING THE DEP FROM RWY 14; I (THE CFI) MADE A CALL ON THE CTAF THAT THE CESSNA MIGHT CONSIDER A GAR IF WE WERE NOT CLR; HOWEVER; THE GROB CLRED RWY 14 WELL AHEAD OF THE CESSNA TWIN LNDG ON RWY 14. DURING THE EVENT; THE FIRST RADIO CALL HEARD WAS THAT THE GROB BETTER CLR THE RWY. WHEN THE CESSNA WAS VISIBLE NO INDICATION OF LNDG LIGHTS WERE APPARENT TO ENHANCE A SAFE OPERATING PRACTICE OF SEE AND BE SEEN. TO ENHANCE SAFETY AT UNCTLED AIRFIELDS; I WOULD SUGGEST AS EARLY AS POSSIBLE A RADIO ADVISORY CALL ON THE CTAF TO ALERT TFC OF THE LOCATION OF THE IFR TFC; THE USE OF ALL AVAILABLE LNDG LIGHTS AND NOT TO ATTEMPT TO DEMAND THE USE OF THE RWY OR ENCOURAGE OTHER ACFT TO HURRY OR EXPEDITE CLRING OF THE RWY SURFACE.