Coach asking ump to get help...

[Bluefoot]

NFHS game. R1 on 1B. R1 steals 2B on pitch. BU is on outfield side of 2B, as R1 slides into 2B. Although F2's throw is caught by F6 before R1 arrives at 2B, R1's foot touches 2B before F6 tag's R1's upper body with glove. BU calls R1 out. All fans, both dugouts, and most importantly, PU, had a better view of play, as BU was shielded from play by F6's body. Offensive coach calmly and politely asks BU if he would please request help on the call from PU, who had a better view. BU replies that no, he will not get help.

The BU is not obligated to ask for help when a coach requests it, correct?

What is the best way for a coach to approach/request one umpire to seek help from a partner on a calls like these, where it is clear that the other umpire had a better view, even if from a farther vantage point?