Is okay to make the following 2 Du'aa:
1) O Allaah, it is against your Glory to put those people in Hell-Fire who are the followers of Allaah and Prophet Muhammad, sallallaahu alayhi wa sallam, and call upon your name (Allaah) therefore, please make the Hell-Fire Haraam on us.
2) O Allaah, accept our Du'aa as a Sadaqah of Prophet Muhammad, sallallaahu alayhi wa sallam.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

First of all, one should not supplicate Allaah saying: "O! Allaah, it contradicts Your Glory to do such or such" as this is a misconduct and rudeness towards Allaah, The Almighty.  Indeed, Allaah is the Best Knower of that which is more appropriate to His Glory and that which is not. 

In fact, some of the believers who abide by the Orders of Allaah and the orders of His Prophet deserve to be sent to Hellfire for some sins that they had committed. Ubay Ibn Ka'b said: "If Allaah punishes all those who are in His Earth or His Heavens, He will do that without being unjust to them.  And if He bestows His mercy upon them, His Mercy will be better for them than their deeds." [Ahmad, Abu Daawood and At-Tirmithi] 

So, how could someone say: "It is inappropriate for Your Greatness or inadequate for Your Glory to send someone to Hellfire…etc?" Allaah Says (what means): {…“Are you more knowing or is Allaah?”…}[Quran 2:140] Allaah also Says (what means): {…And Allaah knows, while you know not.}[Quran 2:16] 

As for saying: "…for the sake of our Prophet ", then if you mean "for the sake of my testifying that he is Your Prophet" then that is acceptable and there is no objection to it because such a testimony is part of belief. Allaah Says (what means): {Those who say, “Our Lord, indeed we have believed, so forgive us our sins and protect us from the punishment of the Fire.}[Quran 3:16]

On the other hand, seeking Tawassul (i.e. seeking nearness to Allaah by virtue of someone or something) from Allaah and supplicating by virtue of one's belief or one's good deeds is lawful as proved in the Quran and the Sunnah. But if what is intended from the mentioned supplication is seeking Tawassul by virtue of the status or glory of the Prophet then such a supplication is not permissible.

Moreover, we advise our Muslim fellows in general to adhere in their supplications to the authentic supplications that have been reported in the Quran or the Sunnah for the great benefit and blessing they encompass and for their covering of comprehensive supplications. Such approach is indeed better than using terms that might be unlawful, like being impolite or transgressing the limits while supplicating.

Abu Daawood reported that 'Abdullaah Ibn Mughaffal heard his son saying: "O! Allaah I ask You to grant me the white palace at the right hand side of Paradise if I enter it." Thereupon, he said to him: "O My son! Ask Allaah for Paradise and seek refuge with Him from Hellfire. I heard the Prophet saying: "There will be amongst this nation, people who transgress the limits in matters of purity (i.e. ablution and Ghusl) and supplication." [Ahmad]

For more benefit on Tawassul, please refer to Fataawa 142097 and 89076.

Allaah Knows best.