The following can be found in the Constitution and Laws of the Most Excellent Grand Royal Arch Chapter of Texas:
Art. C-142 (290-A) Past Master's Degree. Notwithstanding restrictions of these laws to the contrary, a Chapter of Royal Arch Masons under the jurisdiction of the Most Excellent Grand Royal Arch Chapter of Texas may extend an invitation to a member of a Lodge under the jurisdiction of the Most Worshipful Grand Lodge of Texas who is serving or has served as Worshipful Master or while serving as a Warden of a Texas Lodge to receive
only the Past Master's Degree as authorized by this Grand Chapter, excluding those esoteric references to the Mark Master's Degree, under the following conditions: (Amended - 2004)
1 Application to receive the Past Master's Degree shall be made to the Chapter by the completion of a suitable form approved by the Grand Chapter.
2 Application shall be submitted to the Chapter between August 1st and June 23rd of the Masonic Year.
3 The degree may be conferred upon the applicant either during or after his lawful term as Worshipful Master, or while serving as a Warden of a Lodge under the jurisdiction of the Most Worshipful Grand Lodge of Texas. (Amended- 2004)
4 An administration fee of $15.00 shall be collected by the conferring Chapter and forwarded to the Grand Secretary for maintenance of records and preparation of documents pertaining to the degree.
5 The Secretary of the Chapter shall record the conferral in the minutes of the Chapter, and forward the record of conferral to the Grand Secretary.
6 The application, once received by the Chapter and recorded in its minutes may be acted on at a time convenient to the Chapter.
Here is the link to the application referenced above
http://texasyorkrite.org/chapter/forms/lodge/PAST_MASTERS_DEGREE_PETITION.doc
I have never participated in the conferral of the Past Master's Degree in this manner, but I am told that approaching the altar is a bit strange. As said above the work is not altered, portions of the degree from the Mark Master's Degree are omitted, but the flow of the degree is lost a bit.
I have also been told that some lodges in other jurisdictions when the time comes to seat the Master in the east during the installation ceremonies, the brethren are all raised to their feet, all sitting Worshipful Masters and Past Masters are asked to turn and face the east and all other brethren are instructed to turn and face the west. At this time two Past Masters "regularly seat" the brother in his chair.