He cannot wear the ihraam garments – can he enter ihraam in his own clothes?

Yes, if a person is unable to wear the ihraam garments,
then he may wear whatever is suitable of other, permissible clothing.
According to the scholars he has to slaughter a sheep and distribute its
meat to the poor, or feed six poor persons, giving each one half a saa’ of
food, or fast for three days.

This is what the scholars said, by analogy with what was
narrated about shaving the head, as Allaah says (interpretation of the
meaning):

“and do not shave your heads until the Hady reaches
the place of sacrifice. And whosoever of you is ill or has an ailment in his
scalp (necessitating shaving), he must pay a Fidyah (ransom) of either
observing Sawm (fasts) (three days) or giving Sadaqah (charity — feeding six
poor persons) or offering sacrifice (one sheep)”

[al-Baqarah 2:196]

And the Prophet (peace and blessings of Allaah be
upon him) explained that fasting means fasting for three days, giving
Sadaqah (charity) means feeding six poor persons, giving each one half a
saa’, and that sacrificing means slaughtering one sheep. The sacrifice and
feeding of the poor in this case should be done in Makkah, in order to be on
the safe side, because his breaking the rule concerning clothing will last
until he exits ihraam.