You wish is my command. See 4-2-8d in the controllers' manual (7110.65V, CHG 3):
d. When VFR aircraft operating below the
minimum altitude for IFR operations requests an IFR
clearance and the pilot informs you, or you are aware,
that they are unable to climb in VFR conditions to the
minimum IFR altitude:
1. Before issuing a clearance, ask if the pilot is
able to maintain terrain and obstruction clearance
during a climb to the minimum IFR altitude.
PHRASEOLOGY−
(Aircraft call sign), ARE YOU ABLE TO MAINTAIN
YOUR OWN TERRAIN AND OBSTRUCTION
CLEARANCE UNTIL REACHING (appropriate
MVA/MIA/MEA/OROCA)
NOTE−
Pilots of pop−up aircraft are responsible for terrain and
obstacle clearance until reaching minimum instrument
altitude (MIA) or minimum en route altitude (MEA). Pilot
compliance with an approved FAA procedure or an ATC
instruction transfers that responsibility to the FAA;
therefore, do not assign (or imply) specific course guidance
that will (or could) be in effect below the MIA or MEA.
EXAMPLE−
"November Eight Seven Six, are you able to provide your
own terrain and obstruction clearance between your
present altitude and six thousand feet?"
2. If the pilot is able to maintain their own
terrain and obstruction clearance, issue the appropriate
IFR clearance as prescribed in Para 4−2−1,
Clearance Items, and Para 4−5−6, Minimum En
Route Altitudes.
3. If the pilot states that they are unable to
maintain terrain and obstruction clearance, instruct
the pilot to maintain VFR and to state intentions.
4. If appropriate, apply the provisions of
Para 10−2−7, VFR Aircraft In Weather Difficulty, or
Para 10−2−9, Radar Assistance Techniques, as
necessary.
http://www.faa.gov/documentLibrary/media/Order/ATC_7110.65V_chg_3.pdf
(See page 4-2-3.)
The practice was as you have stated it for a while in the 1990s (I think it was), but the alphabet organizations threw a fit, and got the FAA to back down, resulting in approximately the language quoted above. (The changes last month provided clarification, but similar language has existed for years.)
Note that in the above procedure, the aircraft is not even required to be in VFR conditions. Obviously if it is not, the pilot had better have a sound plan for avoiding terrain and obstructions. (The few times I've done it, I've always told ATC how I was planning to avoid the obstacles, so they would have some assurance that I wasn't going to splatter myself on their shift.)