I did just that about 15 years ago. I broke a couple of spokes while tensioning, because the nipples were seized to the spokes.
I just hammered a pair of nail-head replacement spokes into T-head style spokes, worked just fine.

I couldn't even find the exact width guage of nail-head aero spokes anywhere, so I actually ground down the two spoke's aero sections to make the longer dimension of the cross section closer to the original's.

Note that Rovel spoke nipples seated on plastic washers inside the rim. The spokes would lose tension over year's time as these washers slowly compressed/settled.
The spoke re-tensioning was typically hindered by some kind of threadlocker on the threads.

There is also the matter of establishing a spoke-tension specification, which is known to be much lower than spokes of this size would normally be tensioned to, but I have yet to find a number for it.

I arrived at a usable tension by sound and by chance, in the days before I owned a tensiometer, and was able to put a couple of thousand miles on those wheels.

The Roval tubulars had a fairly stiff aero rim, and I remember the clincher version having a very narrow internal width.

On either version, you had to remove the tire to access the spoke nipples for rim truing and/or spoke tensioning.

The axles on Roval's Maillard-built hubs were very fine-threaded for increased resistance to axle breakage, just as on some of Maillard's top-level hubs from the late 70's and early 80's, so replacement parts may be hard to source. I did at one time use a complete axle assembly from another brand of hub, so as to use an 8-speed freewheel, but the fit at the dust covers left a disturbing larger gap.