Referential Constraint Vs Trigger

I am using SQL server 2000. I have a parent table 'MimeTypes' with primary key 'mimetype'. This is referenced as foreign key in table 'AssetTypes' as column 'BaseMimeType'.
The referential constraint is simple :
alter table AssetTypes
add constraint FK_ASSETTYPES_REF_BASEMIMETYPE foreign key (BaseMimeType)
references MimeTypes (MimeType) on update no action on delete no action;

I have FOR Update trigger on parent table ('MimeTypes') which is as follows:

CREATE TRIGGER trg_MimeTypes_update ON MimeTypes FOR UPDATE
AS
IF UPDATE(MimeType)
BEGIN
UPDATE AssetTypes
SET BaseMimeType = (select MimeType from inserted)
FROM AssetTypes as A
JOIN deleted as d on A.BaseMimeType = d.MimeType
END;

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The problem is simple. I want to execute a update query on parent table ('MimeTypes') which modifies 'mimetype' value referenced by child. I dont want to include cascade option in constraint.
When such query is executed error comes as : UPDATE statement conflicted with COLUMN REFERENCE constraint 'FK_ASSETTYPES_REF_BASEMIMETYPE'. The conflict occurred in database 'default.db', table 'AssetTypes', column 'BaseMimeType'.
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Is there any way to do this?