For those of you still interested,

 

Besides what ever limitations (or opportunities) you have negotiated  with the DAR or FAA  airworthiness inspector, one must remember the following:

 

AIM 3-2-2 Class A airspace, para b.Operating Rules and Pilot/Equipment Requirements:  Unless otherwise authorized, all persons must operate their aircraft under IFR.  ....... and Far part 91.167 through 91.193

 

Note: "Unless otherwise authorized"

 

Far Part 91.169 IFR Flight Plan, Info Required: Unless otherwise authorized by ATC........................a.1 Info required under 91.153 (VFR flight plan, same "otherwise authorized by ATC")....................................

 

91.179 IFR Cruising Altitude or Flight Level a. In Controlled Airspace . ...............flight level assigned by ATC .............. If ATC assigns VFR on Top, ....maintain .............. as prescribed in 91.159  .............................

 

91.159 VFR cruising altitude or flight level (note flight level).

 

...................or other authorized by ATC........................  b. When operating above 18000 MSL to flight level 290 inclusive ...............

 

Seems to me the generous use of the phrase "Unless otherwise authorized by ATC" allows one to make the peculiar IFR/VFR request directly to a controller.  Additionally, you may be assigned "VFR on top", even above 18000 feet, without a bottom - in which case you are operating on a IFR flight plan (or not, depending) under VFR (rules) in controlled airspace (class A) and chatting comfortably with ATC (assuming the pilot/equipment requirements are met unless otherwise authorized).

 

I love this stuff. 

 

And flexible rules.