I have cut vocals in the control room with the main monitors blaring, its akin to a live recording with the PA and foldback monitors squealing. The choice is simple, do you go for an inspired performance with a comprimised sound or do you go for the opposite. If the genre of music allows you to place the vocal a liitle further back in the mix, then maybe that is a choice that is worth making.
However if the vocal needs to dominate the mix then the artist, producer , label , management need to understand that there is a tradeoff.
What I have done in the past is to have the small speakers on, flip the phase of one and place the microphone equisdistant form the speakers ( at the apex of a triangle) The singer has to stay on position ( something impossible with a hand held! ) and you can also encourage him to wear in-ears or phones so that he gets a more immediate sense of the mix. Then its a question of balancing the volume of the speakers and headphones. Once the performances are complete, run a pass down where the mic records the intrumental mix at the same volume settings, mic gain and when doing a comp , flip the phase of this track with the vocal track and balance to see if you can get cancellation. At best you will get a result that resembles loud headphone bleed.
On main monitors , it is just not practical or advisable to be reversing the phase of one side. The insistnace of using a hand held mic will only negate any slight reduction in bleed or feedback. You may want to search around to see if there are some stage mics that have a super hypercardiod pattern to mitgate the bleed factor.
But at the end of the day, basic laws of physics are at work and that is the choice.
Good luck, worse thing that can happen is that you get a great vocal take and lose some hearing at the same time !